SRG with German (eRosita) and Russian (ART-XC) X-Ray telescopes was launched by RosKosmos on July 13th of 2019 from Baikonur. During the flight to the L2 point of the Sun-Earth system, SRG performed calibrations and long duration Performance Verification (PV) observations of a dozen of targets and deep fields. Starting in the middle of December 2019, the SRG scanned the whole sky three times....
We experience a golden era in testing and exploring relativistic gravity. Whether it is results from gravitational wave detectors, satellite or lab experiments, radio astronomy plays an important complementary role. Here one can mention the cosmic microwave background, black hole imaging and, obviously, binary pulsars. This talk will concentrate on the latter and new results from studies of...
The fate of massive stars is influenced by the mass lost to stellar winds over their lifetimes, which limit the masses of the stellar remnants that they eventually produce. In this talk I will discuss our recent redetermination of the black hole mass in the X-ray binary system Cygnus X-1. At 21 solar masses, our measurement makes this the most massive dynamically-confirmed stellar-mass black...
A deep absorption in the 21-cm line of atomic hydrogen (HI), redshifted to the epoch of cosmic dawn (z ~ 20), was reported by the EDGES experiment. To explain that absorption trough it has been proposed that either an additional exotic cooling mechanism, or a brighter radio background emission previously unaccounted for is needed. Here we discuss the possibility that the required cosmic radio...
MAGIC is the pioneering imaging air Cherenkov telescopes (IACT) instrument, which started performing high-sensitivity measurements in the sub-200 GeV energy range, down to few 10s of GeVs. Since 2009 MAGIC is operating as a double system of 17m diameter IACTs for performing astrophysical measurements in the very high energy range 30GeV – 100TeV. In recent years, by using novel observation...
The development of the Einstein Field Equations is traced and it is argued that Einstein probably had included the cosmological constant in his field equations but then dropped it at first and later re-inserted it when he needed it for a static cosmological solution of his field equations. His initial derivation would have been geometrical, rather than field theoretic. The significance of this...
Ulugh Beg was the grandson of Tamerlane who conquered a vast area in Transoxania and Iran around 1400. Mohammad Taraghay, best known as Ulugh Beg (lit. “Grand prince”) was born in 1394 in Sultaniya (Zanjan, Iran). In 1409, he became the ruler of Samarkand where he founded a school in 1420 which is still well preserved there. Astronomy was the major subject taught in the school and Ulugh Beg...
We propose a new framework for studying the cosmology of f(R) gravity which completely avoids using the reconstruction programme. This allows us to easily obtain a qualitative feel of how much the ΛCDM model differs from other f(R) theories of gravity at the level of linear perturbation theory for theories that share the same background dynamics. This is achieved by using the standard model...
We consider the problem of asymptotic synchronization of different spatial points coupled to each other in inhomogeneous spacetime and undergoing chaotic Mixmaster oscillations towards the singularity. We demonstrate that for couplings larger than some threshold value, two Mixmaster spatial points $A,B$, with $A$ in the past of $B$, synchronize and thereby proceed in perfect unison towards the...
We investigate simplest composite quantum body – hydrogen atom – in a weak external gravitational field. Using the local Lorentz invariance of spacetime in general relativity, we calculate electron gravitational mass taking into account both kinetic and potential energies of electron in the atom. In addition to the expected change of electron mass due to total energy, we obtain the unexpected...
Current Lorentzian Spinfoams are formulated in terms of a two-complex with spins on faces and intertwiners on edges. In this talk, I discuss how to add a causal structure on wedges. The EPRL model turns out to be given by a sum over these wedge-causal structures. I will show how this sum can be restricted to a single causal configuration and its relation to Engle's proper vertex. [Based on...
We use the CMB, BAO, SN and galaxy weak lensing data to jointly reconstruct the effective dark energy density and the two phenomenological functions (mu and Sigma) describing possible modified gravity effects in the evolution of large scale structure. I will focus on the dependence of such reconstructions on the underlying assumptions (priors) and their implications for dark energy and...
In this talk we will consider several ways to use background radio radiation to learn about the large scale features of our universe as well as fundamental physics. In particular, we will highlight the power in cataloguing and understand a large number of Fast Radio Bursts and their background environments to learn about cosmology.
The last few years have witnessed a great enthusiasm for modified theories of gravity and particularly for scalar-tensor theories. The motivations to modify gravity are to test the limits of general relativity on the one hand and also to propose "answers" to open
questions of cosmology and astrophysics. In this context, many theories have emerged and a very complex landscape of theories...
In my talk I will introduce kappa-deformation of discrete symmetries and I will discuss its phenomenological consequences.
I will provide a critical review of what we learned from the NS-NS merger GW170817 during year of electromagnetic follow up across the spectrum. Specifically, I will focus on recent developments from our coordinated radio-X-ray monitoring campaign that revealed the emergence of a new component of emission.
In 2017, the Event Horizon Telescope (EHT) observed the supermassive black hole M 87* at the center of the giant elliptical galaxy Messier 87 using very-long baseline interferometry between a global network of radio telescopes. Operating at a high radio frequency of 230 GHz, EHT enables imaging of the optically thin emission region in the immediate vicinity of the event horizon of M 87*,...
We propose two models for constant density relativistic perfect-fluid spheres supported by thin shell configurations. These models are obtained from the Schwarzschild constant density star solution: the first via the collapse of the external layers of the fluid into a thin shell by performing a matching with the exterior Schwarzschild solution at a matching radius smaller than the star radius;...
The Hubble constant ($H_{0}$) is one of the most important parameters in
cosmology. Its value directly sets the age, the size, and the critical
density of the Universe. Despite the success of the flat $\Lambda$CDM model, the
derived Hubble constant from Planck data under the assumption of a flat
LCDM model has 4.4-$\sigma$ tension with the direct measurements. If this
tension is not due...
The canonical velocity-dependent one-scale (VOS) model for cosmic string evolution contains a number of free parameters which cannot be obtained ab initio. Therefore it must be calibrated using high resolution numerical simulations. We exploit our state of the art graphically accelerated implementation of the evolution of local Abelian-Higgs string networks to provide a...
Characteristic formulations of General Relativity are based on a null folliation of the spacetime. When combined with the standard Cauchy evolution they can in principle provide highly accurate waveform modelling. During this modelling process it is typical that the full non-linear Einstein field equations are solved numerically. A numerical solution to a PDE problem can converge to the...
The detections of gravitational waves are opening a new window to the Universe. The nature of black holes and neutron stars may now be unveiled, but gravitational radiation may also lead to exciting discoveries of new exotic compact objects, oblivious to electromagnetic waves. In particular, Advanced LIGO-Virgo recently reported a short gravitational-wave signal (GW190521) interpreted as a...
The detection of gamma-ray bursts (GRBs) is one of the main scientific targets pursued by the MAGIC collaboration since almost 20 years. The MAGIC telescopes were specifically designed for this purpose: the main figures of merit are the fast slewing speed (7deg/s), the low energy threshold (~50 GeV at zenith) and the high sensitivity in the low energy regime. These features make MAGIC one of...
I present a method to estimate H(z)/H_0 without assuming a cosmological model. The method employs the clustering of standard candles from future surveys like LSST. We find that LSST can constrain H(z)/H_0 up to z=0.7 with uncertainties, in the best cases, around 5%. The method can be further improved by including large galaxy surveys.
The isotope shifts (IS) in the frequency of an atomic transition are approximately linearly correlated with the shifts in another transition. This linearity is reflected in the so-called King-plot analysis. It has been suggested to search for deviations from linearity as a way to probe beyond-Standard-Model interactions mediated by light bosons [1]. These searches require availability of...
I will review the present status of massive and clustered PBH that may constitute all of the Dark Matter in the Universe.
In this talk, we shall present our studies of a recently-proposed model of spherically symmetric polymer black/white holes by Bodendorfer, Mele
and M\"unch (BMM), which generically possesses five free parameters. However, we find that, out of these five parameters, only three independent combinations
of them are physical and uniquely
determine the local and global properties of the...
Many accreting black holes in Nature are observed to have relativistic jets, and it has been suggested that the jets receive much of their power from the spin energy of the central black hole. There is considerable evidence in support of this idea from computer simulations of accretion flows. The talk will review some recent progress in this field.
Searching for fast radio bursts with MeerKAT will be discussed.
I will discuss two less-discussed, yet physically-motivated channels for EM counterparts of gravitational wave events: brief FRB-like signals from charged CBCs (especially binary black hole mergers and plunging neutron star - black hole mergers) and short-GRB-less X-ray transients. I will also discuss the physical processes that contribute to the delay timescale between CBC signals and their...
In relativistic quantum mechanics, the point spectrum of the Dirac Hamiltonian with Coulomb potential famously agrees with Sommerfeld's fine structure formula for Hydrogen. In the Coulomb approximation, the proton is assumed to only have an electric charge. However, the physical proton also appears to have a magnetic moment. The resulting hyperfine structure of Hydrogen is computed...
The joint observation of GW170817 and GRB 170817A has provided the long sought for conclusive evidence for the connection between binary neutron star mergers and short-hard gamma-ray bursts. Following an overview of the observation of GW170817 by the LIGO-Virgo Collaboration, and of the observations of GRB 170817A by Fermi-GBM and INTEGRAL SPI-ACS, this talk reviews the unambiguous...
We reconsider the thermodynamics of AdS black holes in the context of gauge-gravity duality. In this new setting where both the cosmological constant $\Lambda$ and the gravitational Newton constant $G$ are varied in the bulk, we rewrite the first law in a new form containing both $\Lambda$ (associated with thermodynamic pressure) and the central charge $C$ of the dual CFT theory and their...
I will review current cosmological applications of Type Ia Supernovae (SN Ia) to measure the Hubble constant and constrain the nature of dark energy, with an emphasis on the limiting factors in these measurements. I will describe how near-infared observations of SN Ia provide an alternate path for future supernova cosmology. Astrophysical systematic uncertainties arise from our lack of...
In recent years, there is a renewed debate about the origin of the observed prompt emission signal. Some authors found that synchrotron emission can dominate the spectra of several long bursts, and a recent analysis show that it may be possible to overcome the famous 'line of death' argument by a direct fitting procedure. On the other hand, several recent works showed that non-dissipative...
The Event Horizon Telescope collaboration has released 1.3mm interferometric observations of the core of the galaxy M87. I will review the observations and the general physical principles involved in their interpretation. After describing the basic heuristics needed to understand the effect of a black hole on the observational appearance of nearby emission, I will emphasize that...
Combined influence of linear boost and rotation of a black hole can distort an ambient magnetic field to the extent that magnetic field lines develop a neutral point, where the magnetic intensity vanishes. This purely geometrical effect interacts with the accretion flow that can carry and distort the frozen-in magnetic lines, too. Near the event horizon, the magnetic null is threaded by a...
We study the mode decomposition of the unitarily evolving wave packet constructed for the quantum model of spherically symmetric dust collapsing in marginally bound Lemaître-Tolman-Bondi (LTB) model. We consider the model developed by Kiefer et al. [Phys.Rev.D 99 (2019) 12, 126010], where black hole singularity is replaced by a bounce from collapsing phase to expanding phase in the quantum...
Gravitational waves are usually described in terms of a transverse and traceless (TT) tensor, which allows to introduce the so-called TT coordinates. However, another possible approach is based on the use of a Fermi coordinates system, defined in the vicinity of the world-line of an observer arbitrarily moving in spacetime. In particular, Fermi coordinates have a direct operational meaning,...
The redshifted 21 cm line of neutral hydrogen is one of the most useful probes of the early universe. Several experiments are ongoing and are being planned to detect the signal from high redshifts. Detection of the signal will help in understanding the first stars in the Universe, the formation and evolution of galaxies and also constraining cosmological parameters. In this talk, we will...
We consider a class of exact solutions of Einstein's equations that describe a black hole mimicker for which the relativistic description would fail close to the horizon scale. We investigate how such an hypothetical object may be distinguished from a black hole via observations.
One of the challenges in numerical relativity is to include future null infinity in the computational domain with a well-posed formulation. Success will not only enable us to evolve any system of astrophysical interest, e.g. binary black holes and extracting the gravitational wave signal at future null infinity, with any desired accuracy, but also help in studying various phenomena of...
In 2017, the Event Horizon Telescope (EHT) observed the black hole at the center of the giant elliptical galaxy, Messier 87 using very-long baseline interferometry between a global network of radio telescopes. The resulting linearly polarized images of the accretion flow near the horizon of the black hole (M 87*) show resolved polarized structure with a spiral pattern in the electric vector...
Fast radio bursts (FRBs) are amongst the most energetic objects in our Universe, but despite a number of plausible models, their origin remains a mystery. Thanks to recent advances using the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope we can now routinely localise FRBs to the galaxies they originate form, and in some cases even pinpoint the burst to a region within the...
We study the hydrodynamic representation of the Dirac equation in arbitrary curved space-times coupled to an electromagnetic field. Using a generalized Madelung transformation we derive an integral of the corresponding Bernoulli equation for ferminos and show the corresponding Bernoulli equation. Using the comparison of the Dirac and the Klein-Gordon equations we derive the balance equations...
The evolution of cosmic strings, in particular cosmic string loops, has been an open question for a number of years. The dynamics observed by field theory lattice simulations and by the Nambu-goto approximation do not agree, giving big differences in the lifetimes of loops, which for example affects their gravitational wave production.
In this talk we will discuss the results obtained from...
Despite substantial progress in theoretical modeling and numerical simulations over the past years, our understanding of the physical mechanism of Type Ia supernovae remains incomplete. This has two main reasons. (i) The progenitor systems from which these explosions arise have not been identified, and therefore the initial conditions for the explosion simulations are uncertain. (ii) Modeling...
The late time cosmic acceleration is one of the most puzzling phenomena in modern cosmology. Its modeling within General Relativity (GR) through the cosmological constant (L) results in the LCDM scenario. Although the latter gives a precise description of the Universe, it is known that it still contains a number of unresolved problems. These lead researchers to look for modified gravity...
Thermal evolution of neutron stars is studied in the $f(R)=R+\alpha R^{2}$ theory of gravity.
We first describe the equations of stellar structure and evolution for a spherically symmetric spacetime plus a perfect fluid at rest.
We then present numerical results for the structure of neutron stars using four dense matter equations of state and a series of gravity theories for
$\alpha$...
The second Bianchi identity is a well-known and fundamental differential identity which holds on any smooth (semi-)Riemannian manifold. In general relativity, due to the relation of the curvature tesnor and the energy-momentum tensor via the Einstein equations, this identity then naturally implies energy and momentum conservation for matter fields. What happens in situations where curvature...
Since their discovery in the late 1960s Gamma-Ray Burst (GRB) emission has been deeply investigated with the help of the huge amount of data collected covering the entire electromagnetic spectrum. This large and broadband dataset was essential to constitute a general picture describing the GRB physics, revealing the most credible underlying physical processes and environmental conditions...
An interacting vacuum, with fixed equation of state w=-1, provides a simple model for dark energy in our Universe today, distinct from models with a varying equation of state. I will review the phenomenology of simple models where the vacuum can exchange energy and momentum with dark matter and consider the observational bounds on the interaction coming from the cosmic microwave background and...
Fuzzy dark matter (FDM) is a general term for the lightest possible dark matter particle. FDM is distinct from CDM in manifesting wavelike effects on cosmic scales, which lead to a vast array of methods to probe this model. Across more than 20 orders of magnitude, only two windows windows remain where FDM can constitute the entirety of the dark matter. I will discuss how these windows are...
This talk will report on recent progresses in the simulations of binary neutron star mergers in numerical general relativity with focus on the modeling of merger remnants and electromagnetic counterparts. Applications to the observations of GW170817 and AT2017gfo will be discussed.
Our cosmological discourse is currently dominated by the discrepancy between early and late-time cosmological probes. This tension, if confirmed, can only be resolved by yet unknown physics or by our lack of accounting for systematic uncertainties in the methods. Given the drastic implications of the former, the latter has been of great interest lately. In the context of time-delay strong...
Neutron star mergers have long been believed to drive short-duration gamma-ray bursts, one of the most powerful explosions in the universe. They have also long been believed to be a promising source of the r-process isotopes observed in the Milky Way. These two theories were violently validated in the observation of the first neutron star merger in gravitational waves. The electromagnetic...
In this talk I want to discuss the (unorthodox) scenario when the baryogenesis is replaced by a charge segregation process in which the global baryon number of the Universe remains zero. In this, the so-called axion quark nugget (AQN) dark matter model the unobserved antibaryons come to comprise the dark matter in the form of dense nuggets. In this framework, both types of matter (dark and...
The outcome of a binary neutron star depends sensitively on the mass of the binary and the equation of state of dense nuclear matter. All else being equal, lower mass binaries tend to produce rapidly rotating magnetar remnants that survive longer (if not indefinitely) before collapsing into black holes. I will discuss some of the implications of the resulting diversity imprinted by a range...
I will present recent developments on the geometric analysis of Einstein's field equations for spacetimes containing singularity hypersurfaces, which represent gravitational waves, shock waves, or phase interfaces. I will explain the formulation and classification of scattering laws and junction conditions at singularities, and will discuss bouncing cosmologies (big bang, big crunch). I will...
The Lorentzian EPRL spin-foam model has been shown to asymptote in an appropriate regime to a Regge-like theory of gravity. Analogous results have recently been obtained for the Conrady-Hnybida (CH) extension of the model, but several questions regarding the amplitudes of time-like triangles remain open. In this talk I will present new progress on the asymptotic analysis of such amplitudes, in...
The idea that, after their evaporation, Planck-mass black holes might tunnel into metastable white holes has recently been intensively studied. Those relics have been considered as a dark matter candidate. We show that the model is severely constrained and underline some possible detection paths. We also investigate, in a more general setting, the way the initial black hole mass spectrum would...
A minimal length is generally expected to result in Lorentz-violating dispersion relations. I show how one can formulate a lattice theory that carries a representation of the Poincaré group in the Brillouin zone, and discuss how light cones arise for a subalgebra of observables. [Based on work in collaboration with Bekir Baytaş and Pietro Donà]
Extreme mass ratio inspirals (EMRIs) are expected to be a key source of gravitational waves for the LISA mission. In order to extract the maximum amount of information from EMRI observations by LISA, it is important to have an accurate prediction of the expected waveforms. In particular, it will be necessary to have waveforms that incorporate effects that appear at second order in the mass...
The Planck Legacy Archive (PLA) hosts the products from the European Space Agency mission to study the Cosmic Microwave Background (CMB). The PLA web interface (https://pla.esac.esa.int) directs the users to a wide variety of Planck products, e.g., time ordered data, CMB maps, frequency and astrophysical components maps (Dust, Synchrotron, Free-Free, CIB,..), source catalogues and other...
We apply cosmological reconstruction methods to f(R,T) modified gravity, in its recently developed scalar-tensor representation. We do this analysis assuming a perfect fluid in a Friedmann-Lemaı̂tre-Robsertson-Walker (FLRW) universe. Solutions with general scale factor, curvature parameter and equation of state are found for the energy density, pressure, and one of the dynamical fields of...
We develop new strategies to build numerical relativity surrogate models for eccentric binary black hole systems, which are expected to play an increasingly important role in current and future gravitational-wave detectors. We introduce a new surrogate waveform model, NRSur2dq1Ecc, using 47 non-spinning, equal-mass waveforms with eccentricities up to 0.2 when measured at a reference time of...
We present our studies on the neutrino pairs annihilation into electron-positron pairs ($\nu{\bar \nu}\to e^-e^+$) near the surface of a neutron star in the framework of extended theories of gravity. The latter modifies the maximum energy deposition rate near to the photonsphere and it might be several orders of magnitude greater than that computed in the framework of General Relativity. These...
We will present the extended DeWitt-Schwinger subtraction scheme [1] in order to consistently remove the divergent pieces of the one loop effective action for a scalar field in curved spacetime. This scheme includes a $\mu$ dependence that results in the running of the coupling constants. We will prove that this scheme is compatible with the decoupling of heavy massive fields in the low energy...
The 2017 Event Horizon Telescope (EHT) observations of the core of the galaxy M87 are the first electromagnetic observations probing event horizon scales of a black hole. The data strongly favor an observational appearance dominated by a ring of approximately 40 micro-arcseconds in diameter. However, many interesting questions remain about the appearance of the source. In particular, the...
There has been significant progress in recent years on modelling the evolution of cosmic string and cosmic superstring networks. As we are targeting gravitational wave signals from strings, attention is shifting to the closed string (loop) component of those networks. The predicted signal depends on a number of parameters, some of which are assumed/argued to be of order unity. I will focus on...
Despite years of extensive research, the launching mechanism and the nature of relativistic jets remain open questions. Using 3D RMHD simulations of GRB jets with different initial magnetizations and engine modulation timescales, we calculate the resulting prompt emission light curves by considering photospheric emission and internal shocks, and compare them with observations. Our results show...
In this talk I will review the recent insights into the physics of black hole accretion and jets enabled by the advances in general relativistic numerical simulations. In particular, I will discuss how the jets form, collimate, accelerate, and interact with the ambient medium.
The weak equivalence principle is one of the cornerstone of general relativity. Its validity has been tested with impressive precision in the Solar System, with experiments involving baryonic matter and light. However, on cosmological scales and when dark matter is concerned, the validity of this principle is still unknown. In this talk I will show how relativistic effects in the large-scale...
The photon ring is a narrow ring-shaped feature, predicted by General Relativity but not yet observed, that appears on images of sources near a black hole. It is caused by extreme bending of light within a few Schwarzschild radii of the event horizon and provides a direct probe of the unstable bound photon orbits of the Kerr geometry. The precise shape of the observable photon ring is...
Over the past decade, population studies of fast radio bursts (FRBs) have been challenging to undertake due to the small number of known sources detected with different telescopes and detection pipelines. However, the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) project has now detected a large sample of FRBs which is well suited for such studies. The first...
In the last few years, gamma-ray bursts (GRBs) have been detected at Very High Energy (>100 GeV) gamma rays for the first time since their initial discovery half a century ago. This breakthrough occurred thanks to years of technical and strategic improvements (as well as a bit of good luck). In this talk, I will give an overview of the H.E.S.S. GRB program — how H.E.S.S. follows up GRBs, how...
Arrival-time operators (or observables) describing time-of-flight experiments are naturally constrained by gauge invariance requirements. Surveying the literature on time operators, including POVMs, I will show that a natural generalization of Aharonov-Bohm-Kijowski's arrival-time distribution (referred to as the ``standard arrival-time distribution'' by some authors) fails to be gauge...
The Cosmic Microwave Background temperature and polarization anisotropy measurements have provided strong confirmation of the LCDM model of structure formation. Even if this model can explain incredibly well the observations in a vast range of scales and epochs, with the increase of the experimental sensitivity, a few interesting tensions between the cosmological probes, and anomalies in...
For a flat $\Lambda$CDM (standard) cosmology, a small sample of gravitationally lensed quasars with measured time delays has recently provided a value of the Hubble constant $H_0$ in agreement with data from SNe, but in tension with the Planck flat $\Lambda$CDM result. Identifying biases in some methods may solve this tension, avoiding hasty rejection of the standard cosmological model. As a...
It was found recently that the anisotropies in the homogeneous Bianchi~I cosmology considered within the context of a specific Horndeski theory are damped near the initial singularity instead of being amplified. In this work we extend the analysis of this phenomenon to cover the whole of the Horndeski family. We find that the phenomenon is absent in the K-essence and/or Kinetic Gravity...
We discuss the problem of formation of dark matter (DM) halos from the principle of maximum (coarse-grained) entropy, when including for the quantum nature of the DM particles. In the case of DM fermions, such a formation mechanism involves for (long-range) particle-particle interactions, and can lead to a most-likely phase-space distribution accounting for the Pauli-principle as well as...
The next decade of Universe exploration is expected to undergo a revolution for the transient astrophysics. The third generation of gravitational-wave (GW) observatories, such as Einstein Telescope (ET) and Cosmic Explorer (CE) will allow us for the first time to observe GWs along the cosmic history back to the cosmological dark ages. These observatories will be an unprecedented resource to...
A local population of faint short gamma-ray bursts (GRBs) with late afterglow onset and bright optical kilonova was revealed by the discovery of the first binary neutron star merger GW170817/GRB170817A. In our work we investigate whether similar nearby (<200 Mpc) events were observed by NASA's Neil Gehrels Swift observatory. We selected all the events not associated to any X-ray or optical...
Gaia directly measures the kinematics of the stellar component of the Galaxy with the goal to create the largest, most precise three-dimensional map of the Milky Way (MW).
The very core of the Gaia data analysis and processing involves General Relativity (GR) to guarantee accurate scientific products. Nevertheless, any Galactic model should be developed consistently with the...
The interaction of the Cosmic Microwave Background (CMB) photons with hot electron gas in Galaxy Clusters and surrounding medium can be detected through the Sunyaev Zel'dovich effect. When this effect is detected with high enough angular resolution (~10'') it allows astrophysicists to study the physics of galaxy clusters, relaxed and non-relaxed clusters, and detect filamentary structures...
We study some consequences of the loop quantization of the outermost shell in the Lema\^itre–Tolman–Bondi (LTB) dust spacetime using different quantization strategies motivated by loop quantum gravity. Prior work has dealt with this loop quantization by employing holonomies and the triads, following the procedure in standard loop quantum cosmology. In this work we compare this quantization...
We present new results on the singularity structure and asymptotic analysis of a brane-world that consists of a flat 3-brane embedded in a five-dimensional bulk. The bulk matter is modelled by a fluid that satisfies a non-linear equation of state of the form $p=\gamma\rho^{\lambda}$, where p is the ‘pressure’ and $\rho$ is the ‘density’ of the fluid. We show that for appropriate ranges of the...
The theory of causal fermion systems is an approach to fundamental physics. It gives quantum mechanics, general relativity and quantum field theory as limiting cases and is therefore a candidate for a unified physical theory. The dynamics of causal fermion systems is described by a variational principle called the causal action principle (for more details see...
According to the axial vortical effect, an axial current $J^\mu_A$ is produced in a fluid undergoing a macroscopic vortical motion, which is equal to the local kinematic vorticity $\omega^\mu$ multiplied by the axial vortical conductivity $\sigma^\omega_A$. We probe the curvature corrections to $\sigma^\omega_A$ by computing the thermal expectation value of $J^\mu_A$ with respect to a...
The unprecedented coincident detection of a short gamma-ray burst (GRB) with gravitational waves from a binary neutron star (BNS) merger in GW170817/GRB170817A, followed by the long-lasting broadband afterglow, put our understanding of the structure of GRB jets to the test. GRB170817A turned out to be a particularly interesting event, due to its nearby distance (~40 Mpc) and emission from an...
As detections of mergers of compact bodies begin to flow in, and as we enter an era of precision GW measurements, our understanding of compact bodies, their physics and that of the surrounding astrophysical environment, will continue to grow and at times even be challenged. The need to revise the mass bounds of compact bodies such as BHs and NSs and the possibility of the existence of GW...
Neutron stars in scalar-tensor theories may undergo spontaneous scalarization, which is important for probing the theories with binary pulsar and gravitational wave observations. Since the effect is nonlinear, most studies of spontaneous scalarization were carried out numerically. In the first part of my talk, I explain how one can compute the effect of scalarization analytically based on a...
Although the LCDM model is very successful in explaining current cosmological observations, in light of numerous tensions between data and theory, it is worth investigating the evolution of perturbations in alternative models, especially in the non-linear regime, where future surveys will provide a wealth of data. In this talk I will derive the relevant equations necessary to describe matter...
Major advancements in the study of gamma-ray bursts (GRBs) have arisen in the last few years thanks to the recent detections at very high energy (VHE). In this contribution, the observation of GRB 190829A at VHEs with H.E.S.S. is presented. This GRB is one of the closest-ever detected with a redshift z~0.08, a characteristic that allowed an extended temporal detection from 4 hours to 56 hours...
The first image of the black hole (BH) M87* obtained by the Event Horizon Telescope (EHT) has the shape of a crescent extending from the E to WSW position angles, with a possibly distinct bright hotspot in the ESE sector. We have explored highly simplified toy models for geometric distribution and kinematics of emitting regions in the Kerr metric, assuming that the BH spin vector is fixed to...
Cosmic strings may have formed in the early universe due to the Kibble mechanism. While string networks are usually modeled as being of Nambu-Goto type, this description is understood to be a convenient approximation, which neglects the typically expected presence of additional degrees of freedom on the string worldsheet. Previous simulations of cosmic strings in expanding universes have...
Black holes formation and evolution have been extensively studied at the classical level. However, not much is known regarding the end of their lives, a phase that requires to consider the quantum nature of the gravitational field. A black-to-white hole transition can capture the physics of this phenomenon, in particular the physics of the residual small black holes at the end of the Hawking...
The GRAVITY collaboration has recently a detected continuous circular relativistic motion during infrared flares of Sgr A*, which has been interpreted as orbital motion near the event horizon of a black-hole. In this work, we use the ray-tracing code GYOTO to analyze the possibility of these observations being consistent with a central bosonic star instead of a black-hole. Our model consists...
We report on our progress of an improved test of local Lorentz invariance (LLI) in the electron-photon sector using the highly sensitive meta-stable electronic $F$-state of the $^{172}$Yb$^{+}$ ion [1].
The Zeeman structure of the $F$-state contains two orthogonally oriented orbitals which gives us access to test LLI violation. To suppress the magnetic field noise during the measurement,...
In this talk, I will present my work on cosmography with strong-lensing in galaxy-clusters observed with the Hubble Space Telescope. I will detail some particular aspects of the analysis, in preparation for future surveys like Euclid and CSST.
What the progenitors of Type Ia supernovae (SNe Ia) are, whether they are Chandrasekhar mass or sub-Chandrasekhar mass white dwarfs, has been matter of debate for decades. Various observational hints are supporting both models as the main progenitor. In this talk, I will review the explosion physics and their chemical abundance patterns of SNe Ia from these two classes of progenitors. I will...
We introduce a novel way of measuring H0 from a combination of independent geometrical datasets, namely Supernovae, Baryon Acoustic Oscillations and Cosmic Chronometers, without the need of calibration nor of the choice of a cosmological model. Our method builds on the distance duality relation which sets the ratio of luminosity and angular diameter distances to a fixed scaling with redshift,...
In this talk, I will discuss a cosmological model with dark energy – dark matter interaction. Demanding that the interaction strength $Q_{\nu}$ in the dark sector must have a field theory description, a unique form of interaction strength can be obtained. I will show the equivalence between the fields and fluids for the $f(R,\chi)$ model where $f$ is an arbitrary, smooth function of $R$ and...
Photospheric emission from relativistic outflows may originate in two different regimes: photon decoupling within the outflow or radiative diffusion. I will discuss observed thermal component in the early afterglows of gamma-ray bursts as emission from such diffusive photospheres. In addition, I will discuss implications of photon diffusion for dissipative models of GRBs.
Apertif, the wide-field receiver system currently operating on the Westerbork Synthesis Radio Telescope, offers an unprecedented combination of sensitivity and speed at 1.4 GHz. Its time-domain supercomputing back end (ARTS) performs real-time detection and localisation of Fast Radio Bursts (FRBs). In stand-alone mode, this SKA pathfinder is already the globally most productive 1.4 GHz FRB...
The first imaging of the super massive black hole in M87 by the Event Horizon Telescope (EHT) has marked the beginning of a new era in black hole research that explores the properties through direct image observations. In particular, polarimetric images of the vicinity of black holes have attracted much attention because they reflect the magnetic field structure, which plays a key role in the...
The LAser RAnged Satellites Experiment (LARASE), funded by the National Scientific Committee 2 (CSN2) of the Italian National Institute for Nuclear Physics (INFN) in the years 2013-2019, had among its main objectives that of verifying the gravitational interaction in the weak-field and slow-motion limit of General Relativity. Three geodynamic satellites: LAGEOS (NASA, 1976), LAGEOS II...
I will discuss the general aspects of the Analytic Infinite Derivative (AID) gravity theories. It will be shown in details why an infinite number of derivatives is required to eradicate ghosts. Explicit ghost-free construction will be presented. Then it will be explained how unitarity is maintained in this non-local setup upon accounting loop corrections. Observational aspects will be briefly touched.
AT2017gfo is the first kilonova (KN) that could be extensively monitored in time both photometrically and spectroscopically. Moreover, it is the first optical counterpart of a gravitational wave source and it is associated with the short gamma-ray burst GRB 170817A. Here I present our search for the fingerprints of AT2017gfo-like kilonova emissions in the optical/NIR light curves of 39 short...
A kilonova signal is generally expected after a Black Hole - Neutron Star merger. The strength of the signal is related to the Equation of State of neutron star matter and it increases with the stiffness of the latter. The recent results obtained by NICER suggest a rather stiff Equation of State and the expected kilonova signal is therefore strong, at least if the mass of the Black Hole does...
The thermal Sunyaev-Zeldovich (tSZ) effect is produced by the inverse Compton scattering of cosmic microwave background (CMB) photons by hot electrons, particularly in galaxies clusters. It has been used as a powerful probe to constrain the cosmological parameters, given its particular sensitivity to sigma8 and omega_m.
We present a new all-sky tSZ map constructed from the latest Planck PR4...
Can the 32C-dimensional algebra R(x)C(x)H(x)O offer anything new for particle physics? Indeed it can. Here we identify a sequence of complex structures within R(x)C(x)H(x)O which induces a cascade of breaking symmetries: Spin(10) -> Pati-Salam -> Left-Right symmetric -> Standard model + B-L (both pre- and post-Higgs-mechanism). These complex structures derive from the octonions, then from the...
The long-awaited detection of a gravitational wave from the merger of a binary neutron star in August 2017 (GW170817) marked the beginning of the new field of multi-messenger gravitational wave astronomy. Reaching densities a few times that of nuclear matter and temperatures up to 100 MeV, such mergers also represent potential sites for a phase transition from confined hadronic matter to...
Gravitational-wave(GW) sources can serve as standard sirens to probe cosmology by measuring their luminosity distance and redshift. Such standard sirens are also useful to probe theories beyond General Relativity with a modified GW propagation. Previous studies on the latter assume multi-messenger observations so that the luminosity distance can be measured with GWs while the redshift is...
Following the method presented in the talk "Extended DeWitt-Schwinger subtraction scheme, heavy fields and decoupling [1]", we consider the renormalization of the one loop effective action for the Yukawa interaction with a background scalar field in curved spacetime [2]. We compute the beta functions and discuss the decoupling in the running of the coupling constants. For the case of a...
A cosmological model with Symmetric Teleparallel Gravity where gravity is non-metrical is constrained with redshidt space distortions data. The cosmological background for the model mimics a ΛCDM evolution but differences arise in the perturbations. The linear matter fluctuations are numerically evolved and the study of the growth rate of structures is analysed in this cosmological setting....
Radio-loud quasars (RLQs) are typically more X-ray luminous, by a factor of 2-20, than matched radio-quiet quasars (RQQs). This excess X-ray emission has generally been attributed to small-scale jets. To determine the nature of this excess X-ray emission, we have constructed a large, uniform sample of 729 optically selected RLQs with high fractions of X-ray detections and radio-slope...
Recent detections of gamma-ray bursts (GRBs) at energies above 100 GeV demonstrate that imaging atmospheric Cherenkov telescopes (IACT) operating in the very high energy range (VHE; E > 100 GeV) can provide insight into the physics of GRBs. By searching for the highest-energy photons emitted by GRBs, these telescopes can help answer questions about the particle acceleration and emission...
We develop a systematic approach to obtain spherically symmetric midisuperspace models with modifications inherited from loop quantum gravity. We obtain a family of effective constraints that satisfy Dirac's deformation algebra and show that (scale-dependent) holonomy corrections can be consistently implemented in the presence of matter with local degrees of freedom. These deformed...
A method will be presented which allows for the numerical computation of the stress-energy tensor for a quantized massless minimally coupled scalar field in the region outside the event horizon of a 4D Schwarzschild black hole that forms from the collapse of a null shell. This method involves taking the difference between the stress-energy tensor for the $in$ state in the collapsing null shell...
The progenitor scenarios of Type Ia supernovae remain a mystery having a crippling effect on the many area that have strong connections to these explosive events (e.g. cosmology, chemical evolution of the Universe, stellar evolution, etc.). The current viable scenarios can be divided into two broad categories: 1) 1.4 M$_\odot$ white dwarves that are likely created in an accretion process and...
It is common to express cosmological measurements in units of Mpc/h. Here, I review some of the complications that originate from this practice. A crucial problem caused by these units is related to the normalization of the matter power spectrum, which is commonly characterized in terms of the linear-theory rms mass fluctuation in spheres of radius 8 Mpc/h, σ8. This parameter does not...
We derive the effective polymer Hamiltonian of gravitational waves propagating on an FLRW background. We overcome the problem of polymerizing a time-dependent system by using a novel approach by using the extended phase space approach. Using the resulting Hamiltonian, we study some of the possible observational consequences of such a polymerized gravitational wave Hamiltonian.
In this talk, I will present some recent results on estimating the performance of quantum optomechanical sensors for searches of modified gravity. Specifically, I will show how we derive the best possible bounds that can be placed on Yukawa- and chameleon-like modifications to the Newtonian gravitational potential with a cavity optomechanical quantum sensor. We do so by modelling the effects...
Strongly lensed supernovae (SNe) are emerging as a new probe of cosmology and SN progenitors. The time delays between the multiple images of a lensed SN can be used to determine the Hubble constant (H0) that sets the expansion rate of the Universe. An independent determination of H0 is important to ascertain the possible need of new physics beyond the standard cosmological model, given the...
The quest for high redshift FRBs is ongoing with telescopes such as FAST and GBT looking for highly dispersed events. If FRB-producing systems exist at early times, such sources would provide new unique ways to probe Cosmic Dawn and Reionization. On one hand, FRB dispersion would allow us to probe the history and topology of Reionization. On the other hand, number counts of high redshift FRBs...
We study the axion strings with the electroweak gauge flux in the DFSZ axion model and show that these strings, called the electroweak axion strings, can exhibit superconductivity without fermionic zero modes. We construct three types of electroweak axion string solutions. Among them, the string with W-flux can be lightest in some parameter space, which leads to a stable superconducting cosmic...
Making a high resolution image of a supermassive black hole shadow is a direct method to verify the theory of general relativity at extreme gravity conditions. Very Long Baseline Interferometry (VLBI) observations at millimeter/sub-millimeter wavelengths can provide just provide angular resolution sufficient to start resolving supermassive black holes, located in Sgr A* and M87. Recent VLBI...
Radio afterglows of neutron star mergers are excellent probes of the fast ejecta (relativistic jets and fast tail of the dynamical ejecta) and provide strong constraints on the inclination angle, ejecta morphology and energetics. This information is complementary to the ejecta mass and composition derived from the early-time UV-optical-infrared emission (called the kilonova/macronova). Radio...
The application of numerical techniques to covariant LQG may able to provide answers to many of the current open questions in theory. In this presentation, I first introduce the formalism currently used to implement numerical computations. I illustrate a recent application of numerical techniques concerning the study of divergences in the EPRL self-energy amplitude, on which so far there were...
I review in this talk the mechanism of Primordial Black Hole (PBH) formation at the end of inflation from an oscillating scalar field. I will first present solutions to the Klein Gordon and Einstein equations in this regime for linear perturbations, as well as long-wavelength nonlinear solutions. I argue that these are indicators of the collapse of inhomogeneities onto PBHs. The tiny black...
A class of naked strong curvature singularities is ruled out in Bakry-Emery spacetimes by using techniques of differential topology in Lorentzian manifolds.
These spacetimes adimit a Bakry-Emery-Ricci tensor which is a generalization of the Ricci tensor. This result supports to validity of Penrose's strong cosmic censorship conjecture in scalar-tensor gravitational theories, which include...
The largest temperature anisotropy in the cosmic microwave background (CMB) is the dipole. The simplest interpretation of the dipole is that it is due to our motion with respect to the rest frame of the CMB (with debate over the possibility of alternative explanations). As well as creating the $\ell=1$ mode of the CMB sky, this motion affects all astrophysical observations by modulating and...
We propose a new approach to the thermodynamics of scalar-tensor gravity and its possible ``diffusion'' toward general relativity, previously regarded as an equilibrium state in spacetime thermodynamics. The main idea is describing scalar-tensor gravity as an effective dissipative fluid and applying Eckart’s first order thermodynamics to it. This gives explicit effective quantities: heat...
A rapidly spinning compact object couples to an ambient curved background via the so-called spin-curvature coupling. In expressing this, one has to deal with the ambiguity of the definition of the center of mass of the body. What is worse, in a Hamiltonian formalism, this choice corresponds to an unphysical "parasitic" degree of freedom in the dynamical system. A solution to this is to apply a...
Dark matter scenarios are being tested at the LHC in the general-purpose experiments through promptly decaying states. In parallel, new dedicated detectors have been proposed for the LHC to probe dark matter portal theories predicting long-lived particles that decay away from the interaction point: MoEDAL-MAPP, MoEDAL-MALL, FASER, CODEX-b, MATHUSLA, AL3X, ANUBIS, milliQan. In addition, the...
We provide a method to calculate the rate of false vacuum decay induced by a black hole. The method uses complex tunnelling solutions and consistently takes into account the structure of different quantum vacua in the black hole metric via boundary conditions. We illustrate the technique on a two-dimensional toy model of a scalar field with inverted Liouville potential in an external...
We present the first numerically stable nonlinear evolution for the leading-order gravitational effective field theory (Quadratic Gravity) in the spherically-symmetric sector. The formulation relies on (i) harmonic gauge to cast the evolution system into quasi-linear form (ii) the Cartoon method to reduce to spherical symmetry in keeping with harmonic gauge, and (iii) order-reduction to...
Physical reasoning give expressions for the Hamiltonian of a system. These Hamiltonians are differential operators that are mostly symmetric in a densely defined domain.
However, to study the dynamics of the unitary group corresponding to a Hamiltonian, it is
required that the Hamiltonian be self-adjoint or essentially self-adjoint. I will present our study
on how the static non-linear...
The spectra of the optical/near-IR counterpart of the GW2017 binary neutron star merger show broad absorption features overimposed onto the continuum, that were interpreted as due to heavy elements formed through r-process nucleosynthesis. However, it is very arduous to identify individually the atomic species, owing essentially to the enormous amount of atomic transitions and to substantial...
Observational measurement of the black-hole spacetime is one of the essential topics in modern physics and astrophysics, since it will lead to a critical test of the theory of general relativity. In general relativity, the spacetime around is uniquely determined by its mass and spin parameter. The mass can be accurately measured by observing orbits of stars or gas dynamics inside the sphere of...
Neutron stars are ideal astrophysical sources to probe general relativity due to their large compactnesses and strong gravitational fields. For example, binary pulsar and gravitational wave observations have placed stringent bounds on certain scalar-tensor theories in which a massless scalar field is coupled to the metric through matter. A remarkable phenomenon of neutron stars in such...
As the new era of GW-led multi-messenger astronomy is ushered in, one may especially expect to catch GW signals from neutron star-black hole (NSBH) mergers and search for associated as-yet undiscovered NSBH kilonova emissions. However, in spite of many efforts for follow-up searches of potential NSBH candidates during the third run (O3) of LIGO/Virgo Collaboration (LVC), no surely EM...
"Dark energy", a matter/energy source whose nature is still not well understood, is widely assumed as an explanation for the observed accelerated expansion of the Universe. The standard model of cosmology, the ΛCDM model, consists of the simplest scenarios in which dark energy is a cosmological constant. Even though it provides an impressive fit to the available cosmic background radiation and...
Satellites and imaging atmospheric Cherenkov telescopes (IACTs) have shown that gamma-ray bursts (GRBs) are capable of producing very-high-energy photons— most notably GRB 190114C, observed up to 1 TeV by the MAGIC telescopes approximately one minute after triggering the Fermi GBM and Swift BAT satellites. Particularly suited to such searches and follow-up studies is the High-Altitude Water...
The interior of a Schwarzschild black hole is quantized by the method of loop quantum gravity. The Hamiltonian constraint is solved and the physical Hilbert space is obtained in the model. The properties of a Dirac observable corresponding to the Arnowitt-Deser-Misner mass of the Schwarzschild black hole are studied by both analytical and numerical techniques. It turns out that zero is not in...
The CALorimetric Electron Telescope (CALET) cosmic ray detector on the International Space Station (ISS) has been in operation since its launch in 2015.
The main instrument, the CALorimeter (CAL), is monitoring the gamma ray sky from ~1 GeV up to ~10 TeV with a field-of-view of about 2 sr for more than five years.
In this paper, we describe the analysis of gamma ray candidate events observed...
The emergence of $R^2$ (Starobinsky) inflation from the semi-classical modification of gravity due to matter quantum fields clearly points out the importance of fundamental physics and the first principles in the construction of successful cosmological models. Along with the observational success, $R^2$ gravity is also an important step beyond general relativity (GR) towards quantum gravity....
Type Ia supernovae (SNe) are some of the most common cosmic transients, yet their progenitors are still not known. I will discuss the sub-Chandrasekhar mass pathway to these explosions, known as the double detonation scenario, where a White Dwarf (WD) is able to explode below the Chandrasekhar mass limit through the aid of an accreted helium shell. An ignition of this helium can send a shock...
The Lewis solutions describe the exterior gravitational field produced by infinitely long rotating cylinders, and are useful models for global gravitational effects. When the metric parameters are real (Weyl class), the metrics of rotating and static cylinders are locally indistinguishable, but known to globally differ. The significance of this difference, both in terms of concrete physical...
In the standard cosmological scenario, no circular polarization is predicted for Cosmic Microwave Background (CMB) radiation. However, in the frame of moving particle, Lorentz symmetry can violate and lead to circular polarization for CMB radiation. We estimate the circular polarization power spectrum $C_l^{V(S)}$ in CMB radiation due to Compton scattering in presence of the Lorentz symmetry...
In the QCD axion dark matter scenario with post-inflationary Peccei-Quinn symmetry breaking, the number density of axions, and hence the dark matter density, depends on the length of string per unit volume at cosmic time $t$, by convention written $\zeta/t^2$. The expectation has been that the dimensionless parameter $\zeta$ tends to a constant $\zeta_0$, a feature of a string network known as...
Context. We study eight different gamma-ray burst (GRB) data sets to examine whether current GRB measurements — that probe a largely unexplored part of cosmological redshift (z) space — can be used to reliably constrain cosmological model parameters.
Aims. We use three Amati-correlation samples and five Combo-correlation samples to simultaneously derive correlation and cosmolog- ical model...
The two-point function for a massless minimally coupled scalar field in the Unruh state is computed for various examples of 1+1 dimensional black holes. It is found that for spacelike separations of the points the two-point function grows linearly in terms of a time coordinate that is well-defined on the future black hole horizon, and for Schwarzschild-de Sitter black holes is also...
One problem of the ΛCDM model is the tension between the S8 found in Cosmic Microwave Background (CMB) experiments and the smaller one obtained from large-scale observations in the late
Universe. The σ8 quantifies the relatively high level of clustering. Bayesian Analysis of the Redshift
Space Distortion (RSD) selected data set yields: S8 = 0.700+0.038
−0.037. The fit has 3σ tension with...
Galaxy cluster strong lensing has numerous applications in cosmology. Thanks to the wealth of multi-wavelength observations of clusters using state-of-the-art observatories, such as the Hubble Space Telescope and the Very Large Telescope, this field is providing significant contributions to the understanding of our Universe. One of the main points that are still not fully understood is the...
MoEDAL-MAPP is a pioneering experiment designed to search for highly ionizing (HIP), feebly interacting (mQP) and long-lived particle (LLP) avatars of new physics in p-p and heavy-ions collisions at the LHC. The MoEDAL baseline detector first took data at LHC’s Run-2. This detector was dedicated to the search for HIPs, such as magnetic monopoles or massive (pseudo-)stable charged particles,...
In this talk, I will present the main features of the solutions to a recently-derived set of dynamical equations that governs the effective dynamics of black holes in loop quantum cosmology which were obtained via a revision of the Hamiltonian calculation underlying the Ashtekar-Olmedo-Singh black hole model. I will analyze the possibility that certain quantum parameters are treated as Dirac...
Spinning black holes have long been suspected to be involved in some of the most extreme astrophysical phenomena such as AGN and their relativistic jets for supermassive black holes, and gamma-ray bursts for stellar-mass black holes. The activity of black holes is often associated with the creation and the launching of a relativistic magnetized plasma jet accompanied by efficient particle...
I will discuss recent analytic results on the stationary accretion of the relativistic collisionless Vlasov gas onto a moving Schwarzschild black hole. The model assumes that the gas obeys the Maxwell-Juttner distribution at infinity. The Vlasov equation is solved formally in terms of suitable action-angle variables in the framework proposed originally by Rioseco and Sarbach. Depending on the...
We present the first application of a hierarchical Markov Chain Monte Carlo (MCMC) follow-up on continuous gravitational-wave candidates from real-data searches. The follow-up uses an MCMC sampler to draw parameter-space points following the F-statistic. As outliers are narrowed down, coherence time increases, imposing more restrictive phase-evolution templates. We introduce a novel Bayes...
The connection between binary neutron star mergers and short gamma-ray bursts (GRBs) was solidified by the simultaneous detection of GW170817 and GRB 170817A. These events were followed by bright kilonova emission arising from the radioactive decay of freshly synthesized r-process ejecta, which were expelled during the neutron star merger. Kilonova emission is a fundamental signature of...
A first approximation to describe the interplay between quantum matter and gravity can be obtained in the quantum field theory on curved spacetimes by studying the back-reaction of a quantum field on the spacetime geometry, using the so-called semiclassical Einstein equation. In this framework, the evaporation of four-dimensional spherically symmetric dynamical black holes can be explained by...
In this work we study the local behavior of geodesics in the neighborhood of a curvature singularity contained in stationary and axially symmetric space-times. Apart from these properties, the metrics we shall focus on will also be required to admit a quadratic first integral for their geodesics. In particular, we search for the conditions on the geometry of the space-time for which null and...
The primordial abundance of lithium is still a subject of controversy, given the disagreement between numerical results and observational estimates. We show how this discrepancy can be undestood in the context of variation of fundamental constants at the epoch of Big Bang Nucleosynthesis. The variation of Newton's constant plays a crucial role. In particular, its interpretation in terms of...
A burst of gravitational waves creates a permanent change in separation between two initially comoving test particles; this is known as the gravitational wave memory effect. Near null infinity, two contributions to the memory effect arise: linear memory, which appears in linearized gravity and is due to changes in conserved quantities, and nonlinear memory, which arises due to the nonlinear...
Quantum gravity effects are traditionally tied to short distances and high energies. In this talk I will argue that, perhaps surprisingly, quantum gravity may have important consequences for the phenomenology of the infrared. I will center my discussion around a conception of quantum gravity involving a notion of quantum spacetime that arises in metastring theory. This theory allows for an...
In a cubic cosmological simulation box with three-dimensional periodicity, we determine the gravitational potential and force generated by a single particle. Using both the Newtonian approximation and Yukawa law of gravity within the cosmic screening approach [1,2], we zoom into the regions in the box where the distinction among them becomes significant. Extending the analysis to corresponding...
This talk describes how the Barbero--Immirzi parameter deforms the SL(2,R) symmetries on a null surface boundary. Our starting point is the definition of the action and its boundary terms. We introduce the covariant phase space and explain how the Holst term alters the symmetries on a null surface. This alteration only affects the algebra of the edge modes on a cross-section of the null...
Very long baseline interferometry (VLBI) probes cosmic phenomena at the highest angular resolution in astronomy, with the present record set at about 10 microsecond of arc. This record is achieved in space VLBI (SVLBI) observations of the Russian-led RadioAstron mission which combined a worldwide array of radio telescopes with a 10-m antenna in orbit around the Earth. Continuing on the path of...
We give a lower bound for the ADM mass of 3-dimensional asymptotically flat initial data sets for the Einstein equations. The bound is given in terms of linear growth `spacetime harmonic functions' in addition to the energy-momentum density of matter fields, and is valid regardless of whether the dominant energy condition holds or whether the data possess a boundary. A corollary is a new proof...
Gamma-Ray Bursts (GRBs) are energetic transients originating in a violent explosion of a massive star or merger of two compact objects. These explosions create relativistic blastwave whose expansion leads to external shocks. The emission thus produced is the afterglow observed in
GRBs after the prompt emission. The properties of the emitting region i.e. non-thermal
particle spectrum,...
Can a dynamically robust bosonic star (BS) produce an (effective) shadow that mimics that of a black hole (BH)? The BH shadow is linked to the existence of light rings (LRs). For free bosonic fields, yielding mini-BSs, it is known that these stars can become ultra-compact - i.e., possess LRs - but only for perturbatively unstable solutions. We show this remains the case even when different...
Cosmological and astronomical observations indicate that the majority
of mass and energy density of fields in the universe are in a form
which interacts extremely weakly, if at all, with light. The standard
interpretation is the existence of dark matter, commonly thought to be
in the form of particles not part of the standard model of particle
physics. At present a firm detection of such...
GW170817 was detected 3.4 years ago as the first object to have both a gravitational wave and an EM counterpart. It provided the first confirmation of the connection between short gamma-ray bursts and binary neutron star mergers. For almost 3 years, the broadband EM observations of GW170817 from radio to X-rays showed a very well-behaved simple power-law spectrum, with no spectral evolution....
Multi-messenger detections allow us to learn more about the astrophysical sources by probing different physics and also by guiding the astronomers more precisely with low latency follow-ups. We will present the statistically optimal methods for multi-messenger searches and summarize the joint gravitational-wave and high energy neutrino event searches' results of Low Latency Algorithm for...
The Unruh De-Witt detector was introduced originally to give an operational meaning to particle detection in curved spacetimes. This simple two level quantum system interacts with the quantum field through a monopole type coupling, possibly exciting it to the excited state in the process. As the vacuum state of the field depends on global features of the background spacetime, the transition...
We study exact solutions of infinite derivative gravity within the class of so-called almost universal spacetimes. For such an ansatz, the field equations reduce to a single non-local but linear equation which is exactly solvable with the ghost-free choice $\exp(-\ell^2 \Box)$ of the non-local form factor by eigenfunction expansion or using the heat kernel method. This procedure allows us to...
Although the observed GRB prompt emission spectrum is well constrained, the underlying radiation mechanism is not very well understood. We have explored photospheric emission in GRB jets by modelling the Comptonization of fast cooled synchrotron photons whilst the electrons and protons are accelerated to highly relativistic energies by repeated energy dissipation events as well as Coulomb...
We present results from adaptive mesh refinement (AMR) simulations of global cosmic strings. Using the public code, GRChombo, we perform a quantitative investigation of the dynamics of single sinusoidally displaced string configurations. We study a wide range of string energy densities $\mu \propto \ln{\lambda}$, defined by the string width parameter $\lambda$ over two orders of magnitude. We...
According to several observational evidences, the Hot Big Bang Model is the best framework in which to explain the origin and the evolution of the universe. By the way, it is still not the definitive model. Among its weaknesses, we have to count the lack of a satisfying explanation of how baryons and dark matter formed. In this article we attempt to describe these phenomena through a new...
The precise value of Hubble's constant has become one of the most interesting cosmological tensions in recent years. Measurements of H_0 with Type Ia supernovae, in a series of papers by Reiss et al., use a distance ladder of parallax and Cepheid variable stars, and find a value of H_0 which is significantly higher than expected in a LCDM cosmology with Planck CMB parameters. In this work,...
In the last years, thanks to the increased precision of the measurements of the Hubble constant, H0, some tension has emerged between measurements from local and early-Universe probes. Strong gravitational (SL) lenses with measured time delays between the multiple images are yielding a competitive approach to estimate H0, that is independent and complementary to other techniques. Such studies...
We show that loop quantization leads to the emergence of defocusing terms in the expansion and its rate of change, the Raychaudhuri equation. These terms are suppressed in the region far from the singularity but dominate close to that region and prevent both the expansion and its rate from diverging everywhere inside the black hole. This in turn signals the disappearance of the caustic points...
When two Neutron Stars (NSs) merge a multi-band electromagnetic (EM) emission, known as Kilonova (KN), follows. It is believed to be powered by the radioactive decay of ejecta products. In this contribution we discuss how future measurements of KN light curves and spectra could constrain some interesting features of the NSs in the coalescing binary. In particular we will focus on the impact...
In this work we investigate neutron stars (NS) in f (R, T ) gravity
for the case R + 2λT , R is the Ricci scalar, and T the trace of the
energy-momentum tensor. The hydrostatic equilibrium equations are
solved considering realistic equations of state (EOS). The NS masses
and radii obtained are subject to a joint constrain from massive pulsars
and the event GW170817. The parameter λ needs...
I review the arguments supporting the idea that there is an information puzzle in black holes physics. Namely that unitarity is conflicting with local quantum field theory and the equivalence principle. I show that these arguments rely on speculative extra assumptions, justified only by faith in specific hypothesis on quantum gravity. Therefore the black hole information puzzle a problem only...
A millisecond periodicity in the signal of fast radio bursts (FRBs) has long been searched for, as such a signal could be present if these sources are rapidly rotating neutron stars. Here we report a periodic separation of 218 ms at a 6-sigma significance in the single components of a 3-s long FRB detected by the CHIME/FRB experiment. With its nine or more single components, this FRB...
Collapsed structures, or halos, formed in models with self-interacting dark matter (SIDM) have unique properties that distinguish them from structures formed in cold dark matter (CDM). In particular, momentum and energy exchange inside SIDM halos drives the formation of a central core that may eventually undergo core collapse, such that the halo becomes extremely centrally concentrated. We...
My goal in this talk is to address some of the fundamental mathematical questions in the field of relativistic dissipative fluid dynamics. This is an area that has witnessed progress within the physics community but for which many foundational mathematical questions remain open. Some of these problems, such as the study of causality, local well-posedness and breakdown of solutions, are...
GRMHD simulations have been very successful in interpreting observations from M87*. However, they are unable to account for several important features, such as the plasma loading of the jet or the details of non-thermal radiation, from first principles. Kinetic simulations, on the other hand, are well suited to the task. In this talk, I will review what we have learned from these kinetic...
The precedented multi-messenger campaign launch by the gravitational wave (GW) signal GW170817 and the quasi-simultaneous gamma-ray burst GRB170817A, enabled the study of the various transient counterparts, over different energy bands and timescales, and confirmed for the first time, the hypothesis that binary neutron starts are the progenitor of at least a sub-sample of short GRBs, among many...
I will present constraints on the tensor-to-scalar ratio r using Planck data as described in [Tristram et al., A&A, 647, A128 (2021)].
In this paper, we use the latest release of Planck maps (PR4), processed with the NPIPE code, which produces calibrated frequency maps in temperature and polarisation for all Planck channels from 30 GHz to 857 GHz using the same pipeline. We computed...
Black holes power many of the most powerful sources in the universe through their disks, jets and winds. They are powered by their rotational energy (Nature) and by the gravitational energy of accreting gas and stars (Nurture). The balance of these two modes and their implications, will be re-examined in the light of recent, remarkable observations of the nearby galaxy M87 by the Event Horizon...
Gravitationally bound structures composed by fermions and scalar particles known as fermion-boson stars are regular and static configurations obtained by solving the coupled Einstein-Klein-Gordon-Euler (EKGE) system. As it happens for boson stars, there are different families of solutions labelled by the number of nodes in the radial profile of the scalar field; the ground state solutions have...
Fast X-ray Transients (FXRTs) are as-yet unexplained phenomena. They are energetic X-ray flares that last a few tens to a few thousand seconds. Over the past few years, $\sim$30 extragalactic FXRTs have been discovered in Chandra, XMM-Newton, Swift/XRT and eROSITA data. Numerous proposed explanations include a tidal disruption (TDE) of a white dwarf (WD) by an intermediate-mass black hole...
A kilonova signal is generally expected after a Black Hole - Neutron Star merger. The strength of the signal is related to the Equation of State of neutron star matter and it increases with the stiffness of the latter. The recent results obtained by NICER suggest a rather stiff Equation of State and the expected kilonova signal is therefore strong, at least if the mass of the Black Hole does...
A. Perez Martinez1T, M. A. Perez-Garcia1(∗), E. Rodriguez Querts2 and A. Romero Jorge2
Vacuum in presence of magnetic field exhibits birrefrigence. We have obtained this effect from linear correction of dispersion relation of photon travelling perpendicular to the magnetic field valid even for magnetic fields close to...
I will discuss the status of our understanding of singularities in general relativistic spacetimes. I will cover briefly their definition, location, and existence, while focusing on their classical and quantum nature. I will emphasize what we know, and what we do not know about the effect of test particles and waves on a zoo of singularities, from quasiregular to nonscalar curvature to scalar...
Long gamma-ray bursts are associated with the core-collapse of massive, rapidly spinning stars. However, the believed efficient angular momentum transport in stellar interiors leads to predominantly slowly-spinning stellar cores. In this talk, I will report on binary stellar evolution and population synthesis calculations, showing that tidal interactions in close binaries not only can explain...
Revolutionary progress is underway in the ability to detect CP-violating electric dipole moments (EDMs) of particles such as the electron and proton. I will describe recent searches for the electron EDM that are already sensitive to new physics at scales around 10 TeV. I will also discuss new techniques projected to soon enable orders of magnitude further improvement in the field.
Dark energy might be in charge of the late-time acceleration of the universe, but not only so. Many quintessence models possess scaling or attractor solutions where the fraction of dark energy follows the one of the dominant component in previous epochs of the universe’s expansion. Hence, they could play a role in some physical processes at redshifts z>>O(1). For instance, the presence of a...
In traditional (Dirac quantized) quantum mechanics, Gaussian wave functions play an important role in understanding semi-classicality: they may be chosen to be as sharply-peaked around classical position coordinates and they saturate the uncertainty relation, thereby minimizing quantum fluctuations. Gaussian states may likewise be constructed on the kinematic volume Hilbert space of loop...
Gravitational lensing of fast radio bursts (FRBs) on timescales of nanoseconds to milliseconds is sensitive to the presence of massive bodies up to $100 M_{\odot}$--including brown dwarves, rogue stars, and exotic objects like MACHOs or primordial black holes. The CHIME telescope, a widefield low-frequency radio interferometer operating over the frequency range of 400-800 MHz, detects several...
The Advanced LIGO and Advanced Virgo detectors are now observing large numbers of gravitational-wave signals from compact binary coalescences, with 50 entries in the latest transient catalogue GWTC-2. The next detector upgrades will continue bringing rapidly growing event rates and redshift range, so our chances become better both to detect rare astrophysical effects on these novel cosmic...
We study the gravitational field of ultrarelativistic spinning objects (gyratons) in a modified gravity theory with higher derivatives. In particular, we focus on a special class of such theories with an infinite number of derivatives known as “ghost-free gravity” that include a nonlocal form factor such as exp(-\Box\ell^2), where \ell is the scale of nonlocality. First, we obtain solutions of...
Magnetic reconnection in current sheets is conjectured to power bright TeV flares from the black hole in the center of the M87 Galaxy. It is unclear how, where, and when current sheets form in black-hole accretion flows. We show extreme resolution 3D general-relativistic magnetohydrodynamics and 2D general-relativistic particle-in-cell simulations to model reconnection and plasmoid formation...
The Lambda-Cold Dark Matter ($\Lambda$CDM) model agrees with most of the cosmological observations, but has some hindrances from observed data at smaller scales such as galaxies. Recently, Berezhiani and Khoury proposed a new theory involving interacting superfluid dark matter with three model parameters in \cite{khoury2015}, which explains galactic dynamics with great accuracy. In the present...
The rich EM phenomenology in the first few hours after a compact object merger encodes the nature of the post-merger remnant, and a wide array of other compelling physics. Unfortunately, the requirement to find, and classify a counterpart within the large GW localization regions before followup with sensitive instruments can begin, excludes access to these first few hours, even for the most...
In this talk, we discuss the existence of a static, spherically symmetric spacetime that is the solution of the Einstein field equations coupled with an electric field obeying the equations of electromagnetism of Maxwell-Bopp-Lande-Thomas-Podolsky for a static point charge. Contrary to what happens with the Reissner-Nordstrom spacetime, it is shown that the electric field energy is finite,...
The high-z submillimeter galaxies (SMGs) can be used as background sample for gravitational lensing studies thanks to their magnification bias (Gonzalez-Nuevo et al. 2017), which can manifest itself through a non-negligible measurement of the cross-correlation function between a background and a foreground source sample with non-overlapping redshift distributions. In particular, the choice of...
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope has detected more than 1,000 fast radio bursts (FRBs) with its dedicated transient-search backend (CHIME/FRB). With the goal of localising 1,000 bursts to ~50mas precision in less than two years, CHIME/FRB is now expanding to include a dedicated very long baseline interferometry (VLBI) array of transcontinental outrigger...
In this contribution we identify two scenarios for the evolutionary branch cut universe. In the first scenario, the universe evolves continuously from the negative complex cosmological time sector, prior to a primordial singularity, to the positive one, circumventing continuously a branch cut, and no primordial singularity occurs in the imaginary sector, only branch points. In the second...
GRB 170817A was markedly dissimilar to any other detected short gamma-ray burst as it was observed off-axis. This was further made evident by the information gained from the accompanying observation of GW170817. The event has since sparked discussion into the short gamma-ray burst beam profile and how it can link the observed luminosity of GRB 170817A with the rest of the observed on-axis...
We present the observations of the first unambiguous magnetar giant flare from outside of our galactic neighborhood. Initially, GRB 200415A was identified as a short GRB, but upon further investigation and observations from additional instruments, we concluded this event was a giant flare from a magnetar located in the Sculptor galaxy, 3.5 Mpc away. The GBM lightcurve shows very fast (shorter...
Assuming only the existence of an apparent horizon and its regularity, we derive universal properties of the near-horizon geometry of spherically symmetric black holes. General relativity admits only two distinct classes of physical black holes, and both appear at different stages of the black hole formation. Using a self-consistent semiclassical approach, we find that the resulting...
On one hand, the formalism developed in thermodynamics of spacetime allows a derivation of Einstein equations from the proportionality of entropy to the area. On the other hand, low energy quantum gravity effects imply a modified entropy formula with an additional term logarithmic in the area. Combining both concepts, I will introduce the derivation of quantum modified gravitational dynamics...
Transient gravitational waves from catastrophic collisions of black holes and neutron stars have been observed by the Advanced LIGO and Virgo in the last few years. Studies are also carried out to look for something different -- the much fainter continuous gravitational radiation emitted by non-axisymmetric spinning neutron stars, or ultralight-boson condensates from spinning black holes. In...
A large fraction of Gamma-Ray Bursts (GRBs) lightcurves (LCs) shows X-ray plateaus. We analyze all GRBs with known redshifts presenting plateaus observed by The Neil Gehrels Swift Observatory from its launch until August 2019. The fundamental plane relation between the rest-frame time and X-ray luminosity at the end of the plateau emission and the peak prompt luminosity holds for all the GRB...
About 99 percent of solar energy is produced through sequences of nuclear processes that convert hydrogen into helium in the so-called pp-chain. The neutrinos emitted in five of these reactions represent a unique probe of the Sun’s internal working and, at the same time, offer an intense natural neutrino beam for fundamental physics research.
The Borexino experiment consists of a large-volume...
We consider static and cylindrically symmetric interior string type solutions in the scalar-tensor representation of the hybrid metric-Palatini modified theory of gravity. As a first step in our study,we obtain the gravitational field equations and further simplify the analysis by imposing Lorentz invariance along the t and z axes, which reduces the number of unknown metric tensor components...
Cosmological Gamma-Ray Bursts (GRBs) are known to arise from distinct progenitor channels: short GRBs mostly from neutron star mergers and long GRBs from a rare type of core-collapse supernova (CCSN) called collapsars. Highly magnetized neutron stars called magnetars also generate energetic, short-duration gamma-ray transients called Magnetar Giant Flares (MGFs). Three have been observed from...
Since its inception, the Bekenstein-Hawking area relation for black-hole entropy has been the primary testing ground for various theories of quantum gravity. However, a key challenge to such theories is identifying the microscopic structures and explaining the exponential growth of microstates, providing a fundamental understanding of thermodynamic quantities. Since entropy is a single number,...
Solar neutrinos provide a sample of electron neutrinos of different energies. They are therefore a unique probe of the electron neutrino propagation through solar matter and for the experimental study of the MSW effect. Borexino, with its unique purity and sensitivity, has been able to study individually all components, extracting the best test of electron neutrino survival probability to...
We take on an extensive study of the rotating hairy Kerr black holes, which encompasses, in particular cases, the Kerr black hole ($\alpha=0$). We investigate ergosphere and shadows of the black holes to infer that their size and shape are affected due to the $l_0$ and are found to harbour a richer chaotic structure. In particular, the hairy Kerr black holes possess smaller size but more...
Neutron-star mergers and their remnants are fascinating both as laboratories for physics at high energies and densities and because of their likely importance for the production of heavy elements. There are several approaches to observing these mergers. First, we can locate the EM counterparts of neutron-star GW events. This was spectacularly successful with GW170817, but despite huge efforts...
We study the effect of compact extra dimensions on the gravitational wave luminosity and waveform. We consider a toy model, with a compactified fifth dimension, and matter confined on a brane. We work in the context of five dimensional (5d) general relativity, though we do make connections with the corresponding Kaluza-Klein effective 4d theory. We show that the luminosity of gravitational...
The giant flares of soft gamma-ray repeaters (SGRs) have long been proposed to contribute to at least a subsample of the observed short gamma-ray bursts (GRBs). We performed a comprehensive analysis of the high-energy data of the bright short GRB 200415A, which was located close to the Sculptor galaxy. Our results suggest that a magnetar giant flare provides the most natural explanation for...
Theories predict continuous gravitational waves may be emitted by rotating neutron stars. We present the results of three wide-band directed searches for continuous gravitational waves from young supernova remnants in the first half of the third Advanced LIGO and Virgo observing run. Using three complementary analysis pipelines, we search fifteen young supernova remnants between 10 Hz and 2...
We perform optial follow-up observations of transients such as gravitational
wave signals and fast radio bursts with the Subaru telescope/Hyper Suprime-Cam (HSC),
which is a wide field camera with a field of view of 1.7deg2. The Subaru/HSC
has the highest light collecting power in unit time among all optical telescopes
currently in operation. In this presentation, I will introduce our...
We provide a prescription to compute the gravitational multipole moments of compact objects for asymptotically de Sitter spacetimes. Our prescription builds upon a recent definition of the gravitational multipole moments in terms of Noether charges associated to specific vector fields, within the residual harmonic gauge, dubbed multipole symmetries. We first derive the multipole symmetries for...
We study hydrodynamical simulations of galaxy formation, based on the GADGET-3 code, and investigate supermassive black hole binaries coalescence at $5.5
Borexino recently detect solar neutrinos from the CNO cycle.
In the talk I will review the experiment, the analysis method, the CNO result and its implications.
After the groundbreaking gravitational wave detections of compact binary mergers, core-collapse supernova explosions of massive stars have come into focus as one of the next big challenges for gravitational wave astronomy. Thanks to increasingly mature simulations, our understanding of the expected time-frequency structure of the core-collapse supernova gravitational wave signal has advanced...
Einstein equations projected on Black Hole horizons give rise to the equations of motion of a viscous fluid. This suggests a way to understand the microscopic degrees of freedom on the Black Holehorizon by focusing on the physics of this fluid. In this talk, we shall approach this problem by building a crude microscopic model for the Horizon-fluid(HF) corresponding to asymptotically flat Black...
Primordial black hole (PBH) is a kind of important Dark Matter candidate of cosmological origin. And it is also a potential seed of supermassive black holes. However, the formation and the astrophysical effects of PBH still remain unclear. From theoretical perspective, the speaker and his collaborators proposed sound speed resonance （SSR） mechanism as an efficient novel effect to produce PBH....
Relativistic protons, at the forward external shock of a GRB relativistic blast wave (RBW) become unstable to converting their energy dynamically into e+e- pairs through the emission of synchrotron radiation by these e+e-pairs when their column density becomes higher than a critical value given by $n R \sigma \Gamma^4 \simeq 2$ ($n$ is the ambient density, $R$ the shock radius, $\Gamma$ the...
The LISA detectability of GWs from supermassive black hole mergers will crucially depend on the physical properties of their host galaxies.
In this talk I will present a semi-analytic galaxy formation model, Delphi, that fully tracks the accretion- and merger-driven hierarchical assembly of the dark matter halo, gas, stellar, and black hole masses of high-redshift (z > 5) galaxies. We...
The direct detection of gravitational wave (GW) from binary black hole (BBH) mergers has set a strong evidence for the general theory of relativity. These observations have enabled researchers to look for various aspects of black hole spacetimes; Gravitational wave memory (GW-memory) is one of such physical effects which has not been detected yet. The GW-memory manifests a permanent...
General Relativity is an extremely successful theory, at least for weak gravitational fields, however, it breaks down at very high energies, such as in correspondence of the initial singularity. Quantum Gravity is expected to provide more physical insights concerning this open question. Indeed, one alternative scenario to the Big Bang, that manages to completely avoid the singularity, is...
The detection of neutrinos produced by pp-chain and CNO-cycle provide us fundamental informations on the thermal stratification and on the chemical composition of the solar core.
These can be used to verify the predictions ot the so-called Standard Solar Models (SSMs), which represent a benchmark for stellar evolution, and to constrain standard and non/standard energy generation and...
We present the current state of the art of observational properties of
the class of ultra-long GRBs and discuss of any potential method to
classify them as ultra-long while the prompt emission is still active.
We also discuss their detectability in light of the new experiments
currently planned.
Hawking radiation remains a crucial theoretical prediction of semi-classical gravity and is considered one of the critical tests for a model of quantum gravity. However, Hawking’s original derivation used quantum field theory on a fixed background. Efforts have been made to include the space-time fluctuations arising from the quantization of the dynamical degrees of freedom of gravity itself...
Core-collapse supernovae are fascinating astrophysical objects for multimessenger studies. Gravitational waves (GWs) are expected to play a role in the supernova explosion mechanism, but their modelling is also challenging due to the stochastic nature of the dynamics and the vast possible progenitors, and moreover, the GW detection from these objects is still elusive with the already advanced...
In 2034, within the rapidly changing landscape of gravitational-wave astronomy, the Laser interferometer Space Antenna will be the first space-based detector that will observe the gravitational spectra in the millihertz frequency band. It has recently been proposed that numerous LIGO/VIRGO sources will also be detectable by LISA. LISA will be able to detect binary black holes from our Milky...
Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the universe. The duration and hardness distribution of GRBs has two clusters, now understood to reflect (at least) two different progenitors. Short-hard GRBs (SGRBs; T90 <2 s) arise from compact binary mergers, while long-soft GRBs (LGRBs; T90 >2 s) have been attributed to the collapse of peculiar massive stars...
The Covariant Canonical Gauge theory of Gravity is generalized by including at the Lagrangian level all possible quadratic curvature invariants. In this approach, the covariant Hamiltonian principle and the canonical transformation framework are applied to derive a Palatini type gauge theory of gravity. The metric gµν, the
affine connection γλµν and their respective conjugate momenta, kµνσ...
A large fraction of gamma-ray burst (GRB) light curves (LCs) exhibit plateaus in their afterglow. Since GRBs phenomena are panchromatic in nature, emitting wavelengths from X-ray to radio, there is opportunity to study GRBs along multiple electromagnetic regimes. In this work, we further investigate more than 130 GRBs that show optical plateaus in their LCs. We confirm the two-dimensional...
Accretion mechanism is one of the most efficient processes by which gravitational potential energy of matter can be converted into energy. This phenomenon provides us with an explanation regarding the huge amount of energy liberated and high luminosities observed in AGN's, X-ray binaries, etc. Therefore, modelling these accretion flows are necessary to obtain a proper picture of the system and...
The CNO cycle consists of a series of nuclear reactions that provide energy in stars. There exist multiple different cycles depending on temperature and relative abundance of elements in stars. In the Sun the CNO cycle is a catalyst cycle where nuclear reactions cycle through carbon, nitrogen and oxygen. Initially, a free proton fuses with a carbon-12 nucleus starting a sequence of reactions...
The detection of gravitational waves from core-collapse supernova explosions is a challenging task, yet to be achieved, in which it is key the connection between multiple messengers, including neutrinos and electromagnetic signals. We present a method for detecting these kind of signals based on machine learning techniques. We tested its robustness by injecting signals in the real noise data...
We investigate radial Rindler trajectories in a Schwarzschild spacetime. We assume the trajectory to remain linearly uniformly accelerated (LUA) throughout its motion, in the sense of the curved spacetime generalisation of the Letaw-Frenet equations. For the Schwarzschild spacetime, we arrive at a bound on the magnitude of the acceleration $|a|$ for radially inward moving trajectories, in...
On 26th August 2020,gamma-ray burst monitor onboard Fermi satellite was triggered by an unprecedented genuinely short burst GRB 200826A which is totally different from either of the previous strange ones. The undoubtedly short duration and its proximity, together with large f parameter, prove its genuine short-duration fact. For more metrics, we immediately exploit the prompt and afterglow...
This abstract is primarily based on my recent papers ApJ 909 (2021) 65 and ApJ 896 (2020) 69.
After predicting many sub- and super-Chandrasekhar limiting mass white dwarfs from the observations of peculiar type Ia supernovae, researchers have proposed various models to explain these two classes of white dwarfs separately. We showed that these two peculiar classes of white dwarfs, along with...
Gamma-Ray Burst (GRB) afterglow emission can be observed from sub-TeV energies to radio wavelengths, though radio afterglows are less common. We examine GRB radio light curves to look for the presence of radio plateaus, resembling the plateaus observed in X-ray and optical light curves. We analyze all published GRBs with observed radio afterglow and fit 64 radio light curves with the broken...
From the theory of the multiverse cosmology，it is possible that our universe collides with other universes locally in its history，which may result in local changes of the curvature of the spacetime．In this paper，we propose a method to probe the multiverse using gravitational wave observations for the first time．Our method firstly makes triangles using two detected gravitational wave sources...
The problem of calculating of redshift of electromagnetic spectrum of the star, moving in the vicinity of Schwarzschild black hole is solved in the framework of General Theory of Relativity. The inverse problem: determining of the parameters of motion of a star from observational data of redshift is considered. The approach that gives possibilities to solve the inverse problem is proposed. The...
We describe an action principle, within the framework of the Eddington gravity, which incorporates the matter fields in a simple manner. Interestingly, the gravitational field equations derived from this action is identical to Einstein’s equations, in contrast with the earlier attempts in the literature. The cosmological constant arises as an integration constant in this approach. In fact, the...
Geoneutrino observation is reviewed.
The latest data of KamLAND and Borexino are included as well as the prospects of
near future experiments.
I will first define the stochastic gravitational-wave background (SGWB) and highlight the method we are using to detect it in the presence of correlated magnetic noise. I will then discuss astrophysical and cosmological sources and report on the current constraints imposed from a non-detection during the first three observing runs of the LIGO/Virgo/KAGRA collaboration. I will also address the...
We propose a possible model of explaining recently discovered short GRB 200826A, unifying this event and normal long GRBs from collapsars. The turbulent nature of relativistic jets is responsible for inhomogeneity, resulting in a lot of patchy emission regions in the jet. If such an emission patch is viewed, a short single pulse is observed, while the usual long GRBs are observed when...
The future spaceborne gravitational wave detector LISA will probe a vast array of gravitational wave sources in the millihertz frequency band. Many of these sources will not be individually resolvable, instead adding incoherently to form stochastic gravitational wave backgrounds or foregrounds. The angular structure of these stochastic signals on the sky can be used to understand the spatial...
Cosmological models and the values of their related parameters are widely debated, due to tension in the results obtained by Planck measurements of the Cosmic Microwave Background (CMB) Radiation in the early universe, and Supernovae Type Ia (SNe Ia) data within the late universe. Therefore, we must also consider high-redshift cosmological probes to properly reconstruct a chronological cosmos...
We consider inflationary scenarios of the supersymmetric quantum cosmology of FRLW models with a scalar field. We use the superfield formalism with a superpotential for the scalar superfield. From the probability amplitude solution of the supersymmetric Wheeler-DeWitt equation, we compute an effective probability density from which we get mean trajectories that are parametrized by the scalar....
When two black holes merge, the late stage of gravitational wave emission is a superposition of exponentially damped sinusoids. According to the black hole no-hair theorem, this ringdown spectrum depends only on the mass and angular momentum of the final black hole. An observation of more than one ringdown mode can test this fundamental prediction of general relativity. Here we provide strong...
Astrophysical neutrinos cover at least 18 orders of magnitude in energy, starting from meV (relic neutrinos) till PeV, the highest energy neutrinos ever detected as of today. Among the possible extraterrestrial sources of antineutrinos are the supernovae explosions, gamma ray bursts, neutron and black hole mergers and solar flares. In the Sun, the conversion of solar neutrinos into...
Close white dwarf binaries within our galaxy are promising sources of gravitational wave signals for Laser Interferometer Space Antenna (LISA). While the majority of such systems are expected to have circular orbits, a small portion of those formed through dynamical channels can have significant eccentricities. Analyzing the gravitational wave signals from these systems requires accurate...
Some particle physics models with an additional U(1) gauge interaction are interesting because those address the origin of neutrino masses. We show that, in a wide class of models, such an extra U(1) gauge symmetry breaking in the early universe can be first-order phase transition and hence generate a detectable amplitude of stochastic gravitational wave radiation in future experiments. We...
Recently, ground-based Imaging Atmospheric Cherenkov Telescopes, such as MAGIC and H.E.S.S., have reported the detection of very-high-energy (VHE) gamma-rays from three gamma-ray bursts (GRB 180720B, 190114C, 190829A). One of them, GRB 190829A, was triggered by the Swift satellite, and about 20000 s after the burst onset the VHE gamma-ray emission was detected by H.E.S.S. with ~ 5 sigma...
A large fraction of gamma-ray Bursts (GRBs) lightcurves (LCs) show X-ray plateaus. We analyze all GRBs with known redshifts presenting plateaus observed by The Neil Gehrels Swift Observatory from its launch until 2019 August. The fundamental plane relation between the rest-frame time and X-ray luminosity at the end of the plateau emission and the peak prompt luminosity holds for all the GRB...
A new type of man-made experiment is precomputed and suggested to enforce the evidence base for general relativity (GR) as the Solar system gravity. We present a detailed analytical and numerical descriptions of a space-probe flight from the Earth towards Venus with Venus’ gravity assist (GA) accelerating the probe to return it to the Earth’s orbit. We demonstrate that any planet’s GA is...
A complete census of baryons in the late universe is a long-standing challenge due to the intermediate temperate and rarefied character of the majority of cosmic gas. To gain insight into this problem, we extract measurements of the kinematic Sunyaev-Zel'dovich (kSZ) effect from the cross-correlation of angular redshift fluctuations, a novel probe that contains precise information about the...
AMS-02 is a magnetic spectrometer operating on the ISS since May 2011. Its large acceptance and long exposure time allows to measure the fluxes of all the nuclear species in cosmic rays up to Iron. I will discuss the most recent AMS-02 measurements of primary and secondary nuclei in cosmic rays and their possible contribution to the understanding of the CR acceleration and propagation in the galaxy.
We study asymptotically flat black holes with massive graviton hair within the ghost-free bigravity theory. There have been contradictory statements in the literature about their existence, but we have been able to construct such solutions within a carefully designed numerical scheme. The masses of stable hairy black holes that would be physically relevant range form stellar values up to...
The Large High Altitude Air Shower Observatory is a new-generation multi-component instrument for TeV-PeV gamma rays and TeV-EeV cosmic rays. Recently, LHAASO has published its first result on the discovery of 12 ultrahigh-energy (E>100TeV) gamma-ray sources at more than 7 sigma confidence level. Among them, there are famous sources like the Crab Nebula, the Cygnus Cocoon, as well as new...
The Mikhail Pavlinsky ART-XC telescope is the hard X-ray instrument with grazing incidence imaging optics on board the SRG observatory which successively works in the orbit from July 2019. The ART-XC telescope is designed to provide the first ever true imaging all-sky survey in the 4-30 keV energy band and to study spectral and timing characteristics of X-ray sources. The review of scientific...
The planet-size network of millimeter antennas Event Horizon Telescope (EHT) has recently delivered images of the surroundings of the supermassive compact object M87* at the center of the galaxy Messier 87. Such images are crucial to better understand the physics at play in a strong gravitational field environment. They might also allow to probe the extreme relativistic effects on the...
In this talk the zoo of the High Mass X-ray Binary
Systems (HMXBs) is presented. Among these I will discuss the X-ray/Be systems and
in particular A0535 + 26/HDE245770. Through the multifrequency
experimental data obtained in long observation campaigns it was
possible to develop a particular model for the aforementioned system
and then a general one that explains the delay between...
We estimate the neutrino emission from the decay chain of the $\pi$-meson and $\mu$-lepton, produced by proton-proton inelastic scattering in energetic ($E_{\rm iso}\geq 10^{52}$ erg) long gamma-ray bursts (GRBs), within the type I binary-driven hypernova (BdHN) model. The BdHN I progenitor is a binary system composed of a carbon-oxygen star (CO$_{\rm core}$) and a neutron star (NS) companion....
We place observational constraints on two models within a class of scenarios featuring an elastic interaction between
dark energy and dark matter that only produces momentum exchange up to first order in cosmological perturbations. The first one corresponds to a perfect-fluid model of the dark components with an explicit interacting Lagrangian, where dark energy acts as a dark radiation at...
One of the most ubiquitous features of quantum theories is the existence of zero-point fluctuations in their ground states. For massive quantum fields, these fluctuations decouple from infrared observables in ordinary field theories. However, there is no "decoupling theorem" in Quantum Gravity, and we recently showed that the vacuum stress fluctuations of massive quantum fields source a red...
The cosmological constant is usually associated with the notion of vacuum energy density in quantum field theory (QFT). Whether $\Lambda$ is a rigid quantity or a dynamical variable has been a matter of debate for many years, especially after the introduction of the general notion of dark energy (DE). In an expanding universe one may expect that $\Lambda$, and the corresponding vacuum...
considering the asymmetric thin-shell wormhole (ATSW) model, we find that the impact parameter of the null geodesics is discontinuous through the wormhole in general and hence we identify novel shadows whose sizes are dependent of the photon sphere in the other side of the spacetime. Furthermore, we shoe evident additional photon rings from the ATSW spacetime. Moreover, a potential lensing...
We explore the phenomenological viability of scenarios, suggested by different approaches to quantum spacetime, where quantum-gravity effects in the propagation of particles are triggered by spacetime curvature/expansion.
We rely on a toy model of curvature-induced Lorentz violation for a preliminary exploration, and we find that, differently from what commonly believed, the double...
The quasi-static approximation (QSA) is a useful tool to get a quick and clear physical understanding of the phenomenology of modified gravity which is encoded in two functions (of scale and time): the effective gravitational constant (describing the modified evolution of matter perturbations) and the slip (parametrizing the relations between the two gravitational potentials). This...
We are using information from a paper deriving a Lorentz-violating energy-momentum relation entailing an exact momentum cutoff as stated by G. Salesi . Salesi in his work allegedly defines Pre Planckian physics, whereas we restrict our given application to GW generation and DE formation in the first 10^-39s to 10^-33s or so seconds in the early universe. This procedure is inacted due to an...
Interaction between the standard model matter and low mass scalar dark matter field may be presented as variation of the fundamental constant while interaction with an axion-like field leads to oscillating effects of violation of the fundamental symmetries including electric dipole moments. New interactions mediated by hypothetical particles produce effects, which may be observed in atomic...
We quantize the two-dimensional projectable Horava-Lifshitz gravity with a bi-local as well as space-like wormhole interaction. The resulting quantum Hamiltonian coincides with the one obtained through summing over all genus in the string field theory for two-dimensional causal dynamical triangulations. This implies that our wormhole interaction can be interpreted as a splitting or joining...
Abstract not provided.
We reduplicate the Book “Dark Energy” by M. Li, X-D. Li, and Y. Wang, given zero-point energy calculation with an unexpected “length’ added to the ‘width’ of a graviton wave just prior to specifying the creation of ‘gravitons’, using the Rosen and Israelit model of a nonsingular universe. In doing so we are in addition to obtaining a wavelength 10^30 times greater than Planck’s length so we...
Lensing by wormholes has been explored by several authors and the demagnification effect has been found as a distinctive signature which is not present in lensing from ordinary matter.
We study compact objects made up by ordinary and exotic matter in binary systems with $1/r^n$ potentials, where $n=2$ corresponds to the Ellis wormhole, both in the symmetric case, where the two lenses have...
We applied the conformal dilaton gravity model on a BTZ-like black hole spacetime in five dimensions using the warped Randall-Sundrum-1 variant.
We find exact $(t,r)$-dependent solutions for the dilaton field and the metric components, written as $g_{\mu\nu}=\omega^{\frac{4}{n-2}}\tilde g_{\mu\nu}$, from the 5D Einstein equations, as well as from the induced 4D Einstein equations on the...
We consider the possibility that the Milky Way’s dark matter halo possesses a non-vanishing equation of state. Consequently, we evaluate the contribution due to the speed of sound, assuming that the dark matter content of the galaxy behaves like a fluid with pressure. In particular, in the galactic core we compare two scenarios: a supermassive black hole in vacuum and a dark...
We discuss a generalised form of an emergent dark energy model with one degree of freedom for the dark energy sector that has the flexibility to include both ΛCDM model as well as the Phenomenologically Emergent Dark Energy (PEDE) model proposed by Li & Shafieloo (2019) as two of its special limits. The free parameter for the dark energy sector, namely Δ, has the value of 0 for the case of the...
We study the shadow cast by rotating black holes surrounded by plasma in the context of the novel 4D Einstein-Gauss-Bonnet theory of gravity. The metric for these black holes results from applying the Newman-Janis algorithm to a spherically symmetric solution. We obtain the contour of the shadow for a plasma frequency model that allows a separable Hamilton-Jacobi equation. We introduce three...
Photon-graviton conversion in a magnetic field is a process that is usually studied at tree level, but the one-loop corrections due to scalars and spinors have also been calculated. Differently from the tree-level process, at one-loop one finds the amplitude to depend on the photon polarization, leading to dichroism. However, previous calculations overlooked a tadpole contribution of the type...
We present the results of synchronous multiwave observations of the intrinsic gamma and optical radiation of the long GRB160625B gamma-ray burst by the MASTER Global Network, the Lomonosov Gamma-Observatory and the Konus-Wind gamma detector. We see traces of quasiperiodic optical pulsations of the intrinsic optical radiation on scales of several tens of seconds. We associate quasiperiodic...
A recently proposed Dynamical Space-time Cosmology (DSC) that unifies dark
energy and dark matter is studied. The general action of this scenario includes a Lagrange
multiplier, which is coupled to the energy momentum tensor and a scalar field which is different
from quintessence. First for various types of potentials we implement a critical point analysis
and we find solutions which lead...
As gravitational waves are now being nearly routinely measured with interferometers, the question
of using them to probe new physics becomes increasingly legitimate. In this article, we rely on a
well established framework to investigate how the complex frequencies of quasinormal modes are
affected by different models. The tendencies are explicitly shown for both the pulsation and...
The CALorimetric Electron Telescope CALET is collecting science data on the International Space Station since October 2015 with excellent and continuous performance. Energy is measured with a deep homogeneous calorimeter (1.2 nuclear interaction lengths, 27 radiation lengths) preceded by an imaging pre- shower (3 radiation lengths, 1mm granularity) providing tracking and 10$^{-5}$...
We investigate a autonomous system analysis in terms of new expansion-normalized variables for homogeneous and anisotropic Bianchi-I spacetimes in $f(R)$ gravity in the presence of anisotropic matter. It is demonstrated that with a suitable choice of the evolution parameter, the Einstein's equations are reduced to an autonomous 5-dimensional system of ordinary differential equations for the...
We study Quantum Gravity effects in cosmology, and in particular that of the Generalized Uncertainty Principle on the Friedmann equations. We show that the Quantum Gravity induced variations of the energy density and pressure in the radiation dominated era provide a viable explanation of the observed baryon asymmetry in the Universe.
We discuss the stability and appearance of an asymmetric thin-shell wormhole supported by positive energy sources within the Palatini f(R) gravity. Such object is build using a matching procedure of two Reissner-Nordström space-times with different masses and charges via suitable junction conditions.
The eROSITA Final Equatorial-Depth Survey (eFEDS) carried out during the Performance Verification phase of the Spectrum-Roentgen-Gamma/eROSITA telescope is designed to provide the first eROSITA-selected sample of clusters and groups and to test the predictions for the all-sky survey in the context of cosmological studies with clusters of galaxies. I will present the first results on groups and...
It is generally believed that General Relativity (GR) is of secondary importance in the explosion of core-collapse supernovae (CCSN). However, as 3D simulations are becoming more and more detailed, GR effects can be strong enough to change the hydrodynamics of the supernova and affect the explosion. Since a 3D simulation in full GR is computationally extremely challenging, it is valuable to...
Recently, a diffuse emission of 1-100 GeV gamma-rays has been detected from the direction of M31, extending up to ~ 200 kpc from its center.
The interpretation of the extended gamma-ray emission by the escape of cosmic rays produced in the galactic disk or in the galactic center is problematic.
Here we argue that a cosmic ray origin (either leptonic or hadronic) of the gamma-ray emission...
In this work we present our latest results using photonic, atomic, and mechanical oscillators to undertake experimental searches for dark matter and tests of fundamental physics. First, we will focus on our recent results on searching for scalar dark matter through frequency comparisons, due to oscillations in fundamental constants [1]. Next we will discuss upconverting low mass axion signals...
The recent results of DAMA/LIBRA–phase2 experiment deep underground at Gran Sasso are presented. The improved experimental configuration with respect to the phase1 allowed a lower software energy threshold. The DAMA/LIBRA–phase2 data confirm the evidence of a signal that meets all the requirements of the model independent Dark Matter annual modulation signature, at high C.L. The model...
The photospheric emission in the prompt emission is the natural prediction
of the original fireball model for gamma-ray burst (GRB) due to the large
optical depth ($\tau >1$) at the base of the outflow, which is supported by
the quasi-thermal components found in several Fermi GRBs. However,
the main origin of the most prompt emission spectrum (photosphere or
synchrotron) is still under...
I will review the current status of primordial black holes and their relation with spectral distortions.
Celebrating the centennial of its first experimental test, the theory of General Relativity (GR) has successfully and consistently passed all subsequent tests with flying colors. It is expected, however, that at certain scales new physics, in particular, in the form of quantum corrections, will emerge, changing some of the predictions of GR, which is a classical theory. In this respect, black...
The dynamic center of our galaxy is known to host a source of TeV gamma rays since the very beginning of the 21st century and a link to the supermassive black hole at the Galactic Center has been speculated on ever since. But not only the point-like source, spatially coincident with SgrA*, can be observed from the ground using the Imaging Air Cherenkov Telescope technique, but also diffuse...
Wide-field optical sky surveys are discovering a remarkable diversity
in how stars merge, collapse and explode. The powering mechanism for
many of these requires a source beyond radioactivity, plausibly a
magnetic, rapidly spinning neutron star. The discovery of
the electromagnetic counterpart to a pair of merging neutron stars
and other rapid transients from merging binary systems...
High energy laser beams and particle beams, such as the one of the Large Hadron Collider (LHC) at CERN, can be used as lab-scale, relativistic sources of gravitational fields. We present a study of the creation and possibility of detection of oscillating gravitational fields from lab-scale, relativistic sources. Lab-based sources allow for signal frequencies much higher and far narrower in...
Geometric optics approximation is sufficient to describe the effects in the near-Earth environment. In this framework a careful analysis of the local standard polarization directions allows to obtain transparent expressions for polarization rotation. We provide a simple estimation of this emitter/observer-dependent phase and give its explicit form in different settings: 1) Considering the...
In this talk I will review recent progress that the SDSS-IV / eBOSS collaboration has made in constraining cosmology from the clustering of galaxies, quasars and the Lyman-alpha forest. The SDSS-IV / eBOSS collaboration has measured the baryon acoustic oscillation (BAO) and redshift space distortion (RSD) features in the correlation function in redshift bins from z~0.15 to z~2.33. These...
Scalar-tensor theories leaving significant modifications of gravity at cosmological scales rely on screening mechanisms to recover General Relativity (GR) in high-density regions and pass stringent tests with astrophysical objects. Much focus has been placed on the signatures of such modifications of gravity on the propagation of gravitational waves through cosmological distances while...
It has been known that the zero modes can contribute towards divergence in the entanglement entropy and the nature of the divergent term
can be either log or log(log). However, a clear understanding of what
leads to these two different forms of zero mode divergence is still lacking.
So, in order to throw some light along this direction, I will talk about how
these two different divergent...
In special relativity (SR) and in general relativity, the energy tensors of a charged medium and its electromagnetic field, ${\bf T}_\mathrm{chg}$ and ${\bf T}_\mathrm{field}$, add to give the total energy tensor ${\bf T}$ obeying $T^{\mu \nu }_{\ \, ;\nu}=0$: one has
${\bf T} = {\bf T}_\mathrm{chg} + {\bf T}_\mathrm{field}$. (1)
In the "scalar ether theory of gravitation" (SET),...
The origin of primordial magnetic fields and baryon asymmetry of the Universe are still unresolved issues and require physics beyond the standard models of cosmology and particle physics. Since both require physics beyond the standard model, there is a possibility that the same new physics can solve both.
In this talk, I will discuss our model, where non-minimal coupling to the Riemann...
I will discuss the observational appearance of wormholes if they were observed by a very long baseline interferometry (VLBI) array such as the Event Horizon Telescope, or some more powerful future VLBI array. Certain properties, like change of the diameter of the critical curve with respect to the Kerr black hole of the same mass are difficult to interpret given typically poor constraints we...
The existence of black holes is one of the key predictions of general relativity (GR) and therefore a basic consistency test for modified theories of gravity. In spherical symmetry, only two classes of GR solutions are compatible with the formation of a regular apparent horizon in finite time of a distant observer. In this talk, I will demonstrate how to derive constraints that any...
The Vector-Tensor theories are a class of alternative theories of gravity that differ from the standard General Relativity (GR) with the presence of a vector field besides the metric. They are studied in attempts to understand spontaneous Lorentz violation, to generate massive gravitons, and as models of dark matter and dark energy. In this talk, I outline how the nature of singularities and...
The DArk Matter Particle Explorer (DAMPE) is a space mission, promoted by the Chinese Academy of Science with the collaboration of Italian and Swiss scientific institutions. Since December 2015, DAMPE orbits at the altitude of 500 km and collects data regularly. The detector is made of four sub-detectors: top layers of plastic scintillators, a silicon-tungsten tracker converter, a deep BGO...
We propose that the free-free spectrum in the CMB frequency range provides the constraint on the dark matter halo formation in the early universe
and the density fluctuations on small scales.
When dark matter halos form, gas in the dark matter halos can be heated
and ionized depending on their virial temperature.
Although such hot ionized gas is cooled and recombined to the neutral state...
Particle creation by strong and time-varying backgrounds is a robust prediction of quantum field theory. Another well-stablished feature of QFT is that classical symmetries do not always extend to the quantized theory. When this occurs, we speak of quantum anomalies. In this talk we discuss the intwining relationship between both predictions. First, we point out that the particle...
In my talk I shall discuss how big is the parameter space of the couplings at the Planck scale leading to correct non-susy unification for the SO(10). To do so have calculated the renormalisation group equations for the model and run them down towards the IR and investigated the effective potential. As it turns out the initial parameters has to lie in the very small intervals and have a huge...
We follow an old hypothesis that there exists an intimate connection between weak interaction and gravity, symbolized by the relationship between the Fermi and Newton’s constants. We analyze the hypothesis that the effect of matter upon the metric that represents gravitational interaction in General Relativity is an effective one. This leads us to consider gravitation to be the result of the...
It was found recently that the anisotropies in the homogeneous Bianchi~I cosmology considered within the context of a specific Horndeski theory are damped near the initial singularity instead of being amplified. In this work we extend the analysis of this phenomenon to cover the whole of the Horndeski family. We find that the phenomenon is absent in the K-essence and/or Kinetic Gravity...
The hypothetical variation of the fine structure constant alpha can be studied in a laboratory by comparing two exceptionally accurate atomic clocks over a long period of time. It is especially convenient when the two clock transitions, sensitive to the variation of alpha are found in the same atom. We identify two such systems, the neutral ytterbium and gold atoms. The Yb I atom has at least...
We consider the following question: may two different black holes (BHs) cast exactly the same shadow? In spherical symmetry, we show the necessary and sufficient condition for a static BH to be shadow-degenerate with Schwarzschild is that the dominant photonsphere of both has the same impact parameter, when corrected for the (potentially) different redshift of comparable observers in the...
We assume that the progenitor of the Crab nebula and of the Crab pulsar, like GRB 190114C is a binary-driven hyper-novae of type I (BdHNe I). In BdHN I the explosion of the supernova as well as of the role of the hypercritical accretion of the SN ejecta onto the binary companion neutron star (NS) and onto the newbornNS (νNS) have central role. The synchrotron emission powered by the...
The search for dark matter (DM) weakly interacting massive particles with noble elements has probed masses down and below a GeV/c^2. The ultimate limit is represented by the experimental threshold on the energy transfer to the nuclear recoil. Currently, the experimental sensitivity has reached a threshold equivalent to a few ionization electrons. In these conditions, the contribution of a...
There has recently been interest in Primordial Black Holes (PBHs) as a dark matter (DM) candidate. Constraints on the PBH abundance is obtained through lensing, accretion, dynamical effects and also the analysis of the gravitational wave (GW) events. PBHs may exist and populate today the galactic halos with a wide mass range, from about 10-14MSun up to thousands, or more, of solar masses....
Abstract: Lorentz Invariance Violation (LIV), as predicted by several quantum gravity models, can manifest in very tiny energy-dependent gradients of light speed in vacuum, dispersing time of flight (ToF) along the path from source to observer for photons of different energy. Despite being suppressed by the Planck energy, LIV effects in the ToF of photons can be amplified by huge cosmological...
Hydrodynamical simulations predict that the cosmic web contains the majority of the missing baryons in the form of plasma, called the warm-hot intergalactic medium (WHIM). However, its direct measurement through X-ray emission has been prevented for decades due to the weakness of the signal and to the complex morphology of cosmic filaments.
We identified more than 15,000 large-scale...
"2020 was a special year for magnetar studies. The first simultaneous detection
of an FRB-like radio burst from a Galactic magnetar and its high-energy counterpart
(FRB/SGR 200428) suggests that magnetars can produce FRBs.
Observations of the short γ-ray burst GRB 200415A, associated with a nearby galaxy
and with properties closely resembling the huge initial pulses of magnetar
giant...
The current interests in the universe motivate us to go beyond Einstein's General theory of relativity. One of the interesting proposals comes from a new class of teleparallel gravity named symmetric teleparallel gravity, i.e., $f(Q)$ gravity, where the non-metricity term $Q$ is accountable for fundamental interaction. These alternative modified theories of gravity's vital role are to deal...
In this talk I will show up-to-date cosmological constraints on the interactions between dark matter and the component that might be driving the current acceleration of the universe. In particular, I will explain what is the status of two different theoretical models: (i) coupled quintessence, with a fifth force between dark matter particles, mediated by a scalar field that plays the role of...
Photons propagating through the Universe acquire the effective mass that depends on the local density of free charges. This means that if a light new particle that mixes with photons (e.g. dark photon or axions) exists in Nature, photons can be resonantly converted into such particles at numerous places along a typical line of sight. In particular, this can result in specific distortions both...
As the electron in the hydrogen atom, a bosonic field can bind itself to a black hole occupying a discrete infinite set of states. When (i) the spacetime is prone to superradiance and (ii) a confinement mechanism is present, some of such states are infinitely long–lived. These equilibrium configurations, known as stationary clouds, are states “synchronized” with a rotating black hole's event...
A recently proposed interesting class of black hole mimickers are the so-called "black-bounce" spacetimes. In static spherical symmetry, a candidate spacetime was explored which neatly interpolates between a classical Schwarzschild black hole, a regular black hole, and a traversable wormhole depending on the value of an additional scalar metric parameter. Since this analysis, the discourse...
The cosmic ray all-particles spectrum is a very important result obtained by the NUCLEON space experiment. This spectrum was directly measured up to energies near 500 TeV. The ground-based experiments provide very large statistics but their results depend on applied models. The NUCLEON experiment allows to compare results of direct measurements and data of ground-based experiments. The...
We discuss equilibration process in expanding universes as opposed to the thermalization one in Minkowski space--time. The goal is to answer the question: Does the equilibrium reached before the rapid expansion stops and has negligible effect on the background geometry? Or stress--energy fluxes in a universe of GUT scale curvature have strong effects on the expansion rate and the equilibrium...
Recently the entanglement entropy between universes has been calculated, an entropy which somehow describes the quantumness of a homogeneous multiverse. The third quantization formalism of canonical quantum gravity is used here. I will show improvements of the results in a more general scenario, studying what happens at critical points of the evolution of a classical universe. We infer the...
We look at Viutilli (1999) write up of a generalized schrodinger equation with its Ricci scalar inclusion, in curved space-time. This has a simplified version in Pre Planckian regime, which leads to comparing a resultant admissible wave function with Bohmian reformulations of quantum physics. As was done earlier, we compare this result with a formulation of a modified ‘Poisson’ equation from...
The universe according to the tetron model consists of invisible tiny constituents, elastically bound with bond length about the Planck length and binding energy the Planck energy.
A tetron transforms as the fundamental fermion(=octonion) representation 8 of SO(6,1). With respect to the decomposition SO(6,1)-->SO(3,1)xSO(3) a tetron possesses spin 1/2 and isospin 1/2, i.e. it represents an...
I will present our imaging study of four-dimensional, string-theoretical, horizonless "fuzzball" geometries. Their microstructure traps light rays straying near the would-be horizon on long-lived, highly redshifted chaotic orbits. In fuzzballs sufficiently near the scaling limit this creates a shadow much like that of a black hole, while avoiding the paradoxes associated with an event horizon....
Lomonosov Moscow State University Universat-SOCRAT program is aimed at using small satellites to monitor space threats
These satellites are equipped with instruments for space radiation monitoring, as well asprototypes of devices for observing transient phenomena in the Earth’s atmosphere.
In particular, two satellites are equipped with scintillation phosphich detectors that detect...
The consistency between the cosmic expansion and growth may hold clues about the nature of the acceleration of the Universe. Using model-independent methods, we reconstruct the growth history from redshift-space distortion and deduce the corresponding expansion history, which we test against supernovae data. Motivated by these results, we then introduce a model of two-component dark energy...
Intermediate Mass Black Holes (IMBHs) are a class of black holes with masses in the range 10^2-10^5 solar masses, which can not directly derive from stellar evolution. Looking for these objects and estimating their abundance is important for understanding the nature and distribution of the Dark Matter in the galactic halo. Since February 2018 to January 2020 the LMC and SMC have been...
The Tunka Advanced Instrument for Gamma-ray and cosmic ray Astrophysics (TAIGA) is a hybrid experiment for the measurement of Extensive Air Showers (EAS) with good spectral resolution in the TeV to PeV energy range. In this domain, the long-sought Pevatrons can be detected. Currently the hybrid TAIGA detector combines two wide angle shower front Cherenkov light sampling timing arrays (HiSCORE...
Cosmic Microwave Background (CMB) is a powerful probe to the Universe which carries signatures of cosmic secrets over a vast range of redshifts. Along with spatial fluctuations, spectral distortions of CMB blackbody are also a rich source of cosmological information. In my talk, I will introduce a new kind of spectral distortion of CMB which can arise due to the conversion of CMB photons into...
From a phenomenological point of view, the singularities of ordinary black hole solutions hint at a breakdown of general relativity. The Bardeen black hole is a prototype of regular black hole solutions, i.e. those which are geodesically complete and avoid a curvature singularity.
The Bardeen solution is generally interpreted as a magnetically or electrically charged solution to gravity...
Gamma-ray bursts (GRBs) are highly variable and exhibit strong spectral evolution. In particular, the emission properties vary from pulse to pulse in multipulse bursts. Here we present a time-resolved Bayesian spectral analysis of a compilation of GRB pulses observed by the Fermi/Gamma-ray Burst Monitor. The pulses are selected to have at least four time bins with a high statistical...
In this work, we explore the existence of traversable wormhole solutions supported by double-layer thin-shells and satisfying the Null Energy Condition (NEC) throughout the whole spacetime, in a quadratic form of the generalized hybrid metric-Palatini gravity. We start by showing that for a particular quadratic form of the action, some of the junction conditions of the theory can be discarded...
Quasinormal modes of massless test scalar field in the background of gravitational field for a non-extremal dilatonic dyonic black hole are explored. The dyon-like black hole solution is considered in the gravitational $4d$ model involving two scalar fields and two 2-forms. It is governed by two 2-dimensional dilatonic coupling vectors $\vec{\lambda}_i$ obeying $\vec{\lambda}_i...
A clock in a higher place ticks faster than one in a lower place in accordance with Einstein’s general relativity. A pair of atomic clocks serve as a quantum sensor for the gravitational potential. The relativistic effects of the 450-meter height difference of a broadcasting tower, Tokyo Skytree, were measured using a pair of optical lattice clocks to verify the general theory of relativity....
Dark Matter particle candidates able to induce nuclear recoils can be
also studied using the so-called directionality technique. This approach is
based on studying the correlation between the nuclear recoils direction and
the Earth motion in the galactic rest frame.
Several experimental techniques to explore the directionality approach
have been proposed. In this talk, a review of such...
In this talk, I’ll discuss ideas for new approaches in the hunt for light dark matter was gas-based detectors. I’ll show that the sensitivity that may be achievable through the process of electron ionisation of gas targets in a Spherical Proportional Counter in very promising, going beyond current exclusion limits. I'll also pay particular attention to the potential benefits of molecular gas targets.
Both QCD and EW eras play essential roles in laying seeds for nucleosynthesis and even dictating the cosmological large-scale structure. Taking advantage of recent developments in ultrarelativistic nuclear experiments and nonperturbativ and perturbative lattice simulations, various thermodynamic quantities including pressure, energy density, bulk viscosity, relaxation time, and temperature...
The LISA interferometer, designed for detecting gravitational waves, lends an opportunity to measure the gravitomagnetic field linked by the device. The expected flux is due to the angular momentum of the sun, but could also have a contribution from the angular momentum of the Milky Way, including the dark halo in which our galaxy is likely to be immersed. According to current models, the...
Motivated by the fact that the null-shell of a collapsing black hole can be described by a perfectly reflecting accelerating mirror, we investigate an extension of this model to mirror semi-transparency and derive a general expression for the corresponding Bogoliubov coefficients. In so doing, we introduce the concept of ''impulsive accelerated mirrors", corresponding to those mirrors that...
Science with SWGO will be discussed.
The Schwarzschild spacetime of positive mass is well-known to possess a unique “photon sphere” – meaning a cylindrical, timelike hypersurface $P$ such that any null geodesic initially tangent to $P$ remains tangent to $P$ – in all dimensions. We will show that it also possesses a rich family of spatially spherically symmetric “photon surfaces” – general timelike hypersurfaces $P$ such that any...
The High Energy cosmic-Radiation Detection (HERD) space mission is now being designed, as a result of an international collaboration
among several chinese and european institutions, to make cosmic ray (CR) direct measurements at the highest possible energies with current technologies.
HERD primary scientific goals include precise measurements of the energy spectra of CR individual species up...
We report multicolor optical imaging and polarimetry observations of the afterglow of the first TeV-detected gamma-ray burst (GRB), GRB 190114C, using the RINGO3 and MASTER II polarimeters. Observations begin 31 s after the onset of the GRB and continue until ∼7000 s postburst. The light curves reveal a chromatic break at ∼400-500 s, with initial temporal decay α = 1.669 ± 0.013 flattening to...
We study here phantom models of dark energy represented by a scalar field and with tracker properties. By means of a change of polar-like of variables, we study a general class of models classified in terms of a set of three free parameters. Upon comparison of the models with observations, and considering Bayesian evidence, our results suggest a preference for phantom-like dark energy and...
The detailed analysis of Planck CMB data has shown the presence of temperature asymmetries towards the halos of several spiral galaxies. This is probably due to the rotation of cold clouds (which we called" virial clouds ") present in the halos, that rotate about the rotational axis of the galaxies. It had been proposed that these are pure hydrogen clouds that should be in equilibrium with...
CMB spectral distortions is one of the cleanest probe for electromagnetic energy injection scenarios in the pre-recombination universe. Energy injection without the addition of extra photons gives rise to CMB spectral distortion below z<2*10^6 due to inefficiency of photon non-conserving processes. During this epoch, Compton scattering is the dominant process which drives the evolution of...
In this talk, the gravitational wave generation by a slowly rotating wormhole with radially pulsating throat is considered. Two types of rotating wormholes are used as the model of the wave generation: the slightly rotating Ellis wormhole and the thin-shell wormhole. The later was made from two Kerr black hole solutions. To treat the problem, the assumption of the slightly rotating is...
In this talk, we shall present our recent studies on a (3+1)-dimensional Ho\v{r}ava-Lifshitz gravity coupled with an anisotropic electromagnetic (EM) field. This model is generated by a Kaluza-Klein reduction of a (4+1)-dimensional Ho\v{r}ava-Lifshitz gravity and it exhibits a remarkable feature that the gravitational waves and the electromagnetic waves, in spite of Lorentz invariance...
We argue that the minimal length uncertainty emerging from the generalized uncertainty principle, in which the gravitational impacts on the noncommutative space are thoughtfully taken into account, modifies the whole spacetime geometry. The resulting spacetime metric tensor consists of the symmetric GR compatible metric tensor $g_{\mu \nu}$ and another term comprising $g_{\mu \nu}$ multiplied...
A new type of exotic X-ray signal from supermassive black holes within galactic nuclei was recently discovered and called Quasi-Periodic Eruptions (QPEs). We have used the eROSITA telescope aboard SRG to systematically search for new QPEs and found two (doubling the sample of known sources) in the first year of operations. The new QPEs brought many new insights, since they were found in two...
The Post Newtonian (PN) expansion of General Relativity (GR) yields a series of potentials that accurately describe the trajectories of compact binaries to a very high degree of accuracy. In the mathematical treatment of PN expansion of GR, a relation is established between the ratio of the orbital velocity to the speed of light and the compactness-to-closeness ratio: the ratio between average...
This abstract is primarily based on my paper EPJC 79 (2019) 877.
$f(R)$ gravity theory is one of the most popular alternate theories of gravity, which has been used to describe various phenomena in cosmology and astrophysics. In this talk, I will explore the properties of spacetime in the presence of $f(R)$ gravity. First, I will describe how it is used to obtain a spherically symmetric...
In this talk, we discuss recent results on neutral fermion pair production from the vacuum by an inhomogeneous Sauter-like magnetic field. We find exact solutions of the Dirac-Pauli equation in this field and calculate differential and total quantities characterizing vacuum instability. Special attention is paid to cases where the gradient of the magnetic field varies either gradually or...
The Fornax dSph displays a variety of globular cluster at projected radii that seem at odds with the presence of a NFW profile. I will quantify this 'anomaly' (at the level of a 25% tuning) and discuss how different DM models can alleviate it.
Due to the general covariance of the Einstein equations and
conservation laws, the linearized equations have solutions which are
gauge-dependent and have, therefore, no physical significance.
In this talk I will show that the decomposition theorems for symmetric
second-rank tensors of the maximally symmetric subspaces of constant
time imply that there are exactly two, unique,...
Consider, in the domain of wormhole, a point $p$ (observation event) and a timelike curve $\gamma$ (worldline of light source).
We prove that for infinitely many positive integers $\kappa$ there is a past-pointing lightlike geodesic $\lambda_{\kappa}$ of Morse index $\kappa$ from $p$ to $\gamma$ , hence an observer at $p$ sees infinitely many images of $\gamma$.
We will show that in the...
In this talk, I will focus on the photospheric emission observed in the short gamma-ray bursts (GRBs). In our work, we find that several short GRBs are consistent with a pure, non-dissipative photospheric model, at least around the peak of the pulse. For these bursts, we find (i) a bimodal distribution in the values of the Lorentz factors and the hardness ratios and (ii) an anti-correlation...
We analyze the Joint Light-curve Analysis (JLA) Type Ia supernovae (SN Ia) compilation implementing the non-parametric iterative smoothing method. We explore the SN Ia light-curve hyperparameter space and find no dark energy model dependence nor redshift evolution of the hyperparameters. We also analyze the more recent Pantheon SN Ia compilation to search for possible deviations from the...
The Heavy Photon Search (HPS) experiment searches for an electro-produced dark photon using an electron beam provided by the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility.
HPS looks for dark photons through two distinct methods, a resonance search in the e+e- invariant mass distribution above the large QED background (large dark photon-SM particles coupling region)...
MASTER Global Robotic Network of Lomonosov Moscow State University is the network of 8 robotic optical telescopes
located all over the world. One of their goals is the search for optical counterparts to short-
living transients such as GRB, gravitational waves and high-energy neutrinos. It is helped by
the fast reaction time of the telescopes on such alerts and their fast slewing. On...
The thermal Sunyaev-Zeldovich (tSZ) effect is produced by the inverse Compton scattering of cosmic microwave background (CMB) photons by hot electrons, particularly in galaxies clusters. It has been used as a powerful probe to constrain the cosmological parameters, given its particular sensitivity to sigma8 and omega_m.
We present a new all-sky tSZ map constructed from the latest Planck PR4...
Taking advantage of the simplicity of the quantum field theory of a free massless scalar field in 1+1 dimensions, a toy model that explores the effects of the interaction of wormholes and quantum fields is constructed. The conditions for the existence of quantum particle production are discussed in terms of the symmetries of the two-point function of the scalar field theory.
Very slow, so-called ultra-cold neutrons form bound quantum states in the Earth's gravitational field. These neutrons allow the fascinating possibility to investigate gravity at short distances using a simple quantum system. A spectroscopy method for ultra-cold neutrons bound to the surface of mirrors allows to drive transitions between eigen-states of quantum gravitational states. This...
The observational evidence for the recent acceleration of the universe shows that canonical theories of cosmology and particle physics are incomplete and that new physics is out there, waiting to be discovered. A compelling task for astrophysical facilities is to search for, identify and ultimately characterize this new physics. I will present very recent developments in tests of the stability...
We examine the radiation emitted by high energy positrons channeled into silicon crystal samples. The positrons are modeled as semiclassical vector currents coupled to an Unruh-DeWitt detector to incorporate any local change in the energy of the positron. In the subsequent accelerated QED analysis, we discover a Larmor formula and power spectrum that are both thermalized by the acceleration....
The evidence is mounting that the Universe is currently undergoing a phase of accelerated expansion. One possible alternative is the modification in gravity in the largest possible scales. This leads to the many questions related to black-holes: violation of Birkhoff theorem and no-hair theorem. To confirm/infirm, we need to obtain exact black-hole solutions in these modified gravity theories....
The Pierre Auger Observatory has by now achieved an exposure of order 10^5 km^2 sr yr, exploring about 85% of the sky. In this talk I will review some of the latest results, including the detailed measurements of the features in the cosmic ray spectrum, the inferred mass composition, the tests of hadronic interactions, multimessenger searches and the study of anisotropies in the cosmic ray...
The Magellanic Clouds are an ideal site to study X-ray source population of a galaxy including supernova remnants, high mass X-ray binaries (HMXBs) and super-soft sources. This is facilitated by their well-determined distances and low foreground absorption conducive for performing detailed studies. The population of HMXBs in the Magellanic Clouds is especially overabundant owing to the...
Geometrothermodynamics (GTD) can be used in relativistic cosmology to generate models of barotropic fluids. As an alternative approach, we use the GTD formalism to find the most general thermodynamic fundamental equations that describe the barotropic fluids of the Lambda-CDM model. This allows us to investigate the thermodynamic properties of these barotropic fluids from the point of view of...
We investigate Horava-Lifshitz Einstein- Aether gravity in light of the recent Event Horizon Telescope (EHT) observations of the M87*. The shape and size of the observed black hole shadow contains information of the geometry in its vicinity, and thus one can consider it as a potential probe to investigate different gravitational theories, since the involved calculation framework is enriched...
The problem of time arising in Quantum Gravity is a core problem for which a common solution is not yet identified. In this talk we will examine the semiclassical approach to the dynamics of a gravity-matter system, with the goal of reproducing the standard quantum field theory on a fixed Wentzel-Kramer-Brillouin metric background and, at the next order of expansion, computing the quantum...
We investigate the combined effect of cosmic magnetic field and a possible non-standard interaction between baryons and dark matter (DM) on the thermal Sunyaev−Zel’dovich (tSZ) effect which depends on the temperature and the ionization state of the intergalactic medium. The drag force between the baryons and DM due to the relative velocity between them, and their temperature difference results...
Magnetic fields observed in galaxies have the toroidal component. We present the hypothesis that such fields maybe remnants of relic magnetic torus - shaped wormholes. Such magnetic wormholes produce the two important effects. The first effect is that in the primordial plasma before the recombination magnetic fields of wormholes trap baryons whose energy is smaller than a threshold energy....
We consider physics beyond the standard model, which incorporates a see-saw mechanism for neutrino masses. This physics is augmented by incorporating gravitational degrees of freedom ( dilaton, graviton and Kalb-Ramond field) found in the theory of closed strings. In the inflationary era the gravitational degrees of freedom and inflatons dominate. Due to quantum effects there is a...
Particles are spontaneously created from the vacuum by time-varying gravitational or electromagnetic backgrounds. It has been proven that the particle number operator in an expanding universe is an adiabatic invariant. In this talk we show that, in some special cases, the expected adiabatic invariance of the particle number fails in presence of electromagnetic backgrounds. In order to do this,...
Various observations have shown that dark energy accounts for nearly two-thirds of the energy density of the Universe.
The simplest model to explain the nature of dark energy is the cosmological constant ($\Lambda$CDM) model. Although Planck observations supports using $\Lambda$CDM model as the base cosmological model, there exist some inconsistencies in parameter estimates when compared with...
We examine if there are grounds to entertain the Penrose suggestion as to black holes from a prior cycle of creation appearing in the present cosmos. There are two cases to consider. One a singular start to the Universe or as Karen Freeze and others have modeled a non-singular start. The two cases are different and touch upon the limits of validity of the Penrose singularity theorem. We will...
Current astrophysical observations show that on large scale the Universe is electrically neutral. However, locally this may be quite different. Black holes enveloped by a plasma in the presence of a strong magnetic field may have acquired a significant electric charge. We can also expect that some of these charged black holes are moving. Consequently to describe them we need spacetime metrics...
- We consider an inverse procedure as to predict what may be obtained in eLISA , near Earth Orbit, in GW frequency. Among other issues would be the duration of the GW pulse so observed, in eLISA measurements, the relative degree of noise in the signal, as observed by eLISA, and this by the device of a step down in frequency of GW from about 10^19 Hz, in the early universe, or at a minimum...
We propose a new method for probing inflationary models of primordial black hole (PBH) production, using only CMB physics at relatively large scales. In these scenarios, the primordial power spectrum profile for curvature perturbations is characterized by a pronounced dip, followed by a rapid growth towards small scales, leading to a peak responsible for PBH formation. We focus on scales...
Within the framework of F(R) theories of gravity with (2+1)-dimensions and constant scalar curvature R, we construct a family of thin-shell wormholes with circular symmetry and we analyze the stability of the static configurations under radial perturbations. We show an example of asymptotically anti-de Sitter thin-shell wormholes with charge, finding that stable configurations with normal...
Due to the quantum origin of primordial perturbations and the energy scales of the primordial plasma, the early universe is an ideal setup for the interplay between gravity, quantum physics and thermodynamics. Even though most of the expansion history of the universe is adiabatic, irreversible processes play a role in key cosmological events. In this talk I will discuss results and ongoing...
Developed as NASA Astrophysics Probe-class mission, the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is designed to identify the sources of ultra-high energy cosmic rays (UHECRs) and to observe cosmic neutrinos with full-sky coverage for both of these extreme- energy messengers. POEMMA consists of two spacecraft flying in a loose formation at 525 km altitudes oriented to view a...
The Standard Model of particle physics is both incredibly successful and glaringly incomplete. Among the questions left open is the striking imbalance of matter and antimatter in our universe, which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision. The BASE collaboration at the antiproton decelerator of CERN is performing such...
The quantum vacuum has long been known to be characterized by field correlations between spacetime points. These correlations can be swapped with a pair of particle detectors, modelled as simple two-level quantum systems (Unruh-DeWitt detectors) via a process known as entanglement harvesting. We study this phenomenon in the presence of a rotating BTZ black hole, and find that rotation can...
A method is described for creating a measurable unbalanced gravitational acceleration using a gravitomagnetic field surrounding a superconducting toroid as described by Forward (1962). An experimental Superconducting Magnetic Energy Storage (SMES) toroid configuration of wound superconducting nanowire is proposed to create a measurable acceleration field along the axis of symmetry, providing...
Some of the most prominent theoretical predictions of modern times, e.g., the Unruh effect, Hawking radiation, and gravity-assisted particle creation, are supported by the fact that various quantum constructs like particle content and vacuum fluctuations of a quantum field are observer-dependent. Despite being fundamental in nature, these predictions have not yet been experimentally verified...
Relations between the neutron star moment of inertia, tidal Love number and quadrupole moment are known to be insensitive to the nuclear equation of state (the so-called I-Love-Q relations). Such universal relations are powerful for testing general relativity and beyond in the strong-field regime with neutron star observations. Horava-Lifshitz gravity is one such alternative theory of gravity...
Being located at only ~8 kpc from us, the center of our Galaxy provides us with the unique opportunity to study the physics occurring in the core of normal galaxies at very high spatial resolution. Thanks to its penetrating power, the X-ray band is particularly suited for studies of the Galactic center, allowing us to have a direct view of the central heart of the Milky Way. The outstanding...
The dissipation of primordial perturbation modes with wavenumbers $50\,{\rm Mpc}^{-1} < k < 10^4 \,{\rm Mpc}^{-1}$ in the early Universe cause $\mu$-type spectral distortions to the average CMB blackbody radiation. Besides, some inflation scenarios (multi-field or single-field inflation with modified initial state) predict large primordial non-Gaussianity at these scales, so that non-Gaussian...
In this work, we explore wormhole geometries in a recently proposed modified gravity theory arising from a non-conservative gravitational theory, tentatively denoted action-dependent Lagrangian theories. The generalized gravitational field equation essentially depends on a background four-vector $\lambda^\mu$, that plays the role of a coupling parameter associated with the dependence of the...
From previous work, Phys. Rev. D 103, 105003 (2021), the semiclassical backreaction equation (SBE) in 1+1 dimensions was solved and a criterion was implemented to assess the validity of the semiclassical approximation in this case. The criterion involves the behavior of solutions to the linear response equation (LRE) which describes perturbations about solutions to the SBE. The LRE involves...
One of the surprising properties of black holes is that they can be assigned an entropy proportional to the area of the horizon. With this assignment, black holes obey the laws of thermodynamics.
Over the last decade, a new type of black hole entropy entropy formula was developed which is believed to give the von Neumann or fine grained entropy of the black hole. It is also a formula...
Hawking showed that the von Neumann or fine-grained entropy of the radiation emanating from an evaporating black hole monotonically increases throughout the black hole’s lifetime. This suggests that black hole formation and evaporation can evolve a pure quantum state of a collapsing star into a mixed quantum state of the Hawking radiation. This is in direct conflict with the unitarily of time...
In using QFT to study black holes, coordinate transformations are needed with boundary conditions at the horizons. To avoid quantum copies it is imperative that the mapping must be one-to-one. It is explained why this turns the horizons into projective spheres instead of regular spheres. Also what is needed is the concept of `antivacuum', a state on which all creation operators vanish. This...
I will review recent progress on our understanding of the issue of strong cosmic censorship in general relativity, including very recent developments in the case of non-zero cosmological constant.
I will talk about my very recent result in collaboration with Jeremie Szeftel in which we provide a complete proof of the nonlinear stability of the family of Kerr spacetimes Kerr(a, m) with small a/m. The proof, which builds on our previous work `` Global non-linear stability of Schwarzschild space under polarized perturbations’’ , introduces various new geometric and...
Singularity theorems of Penrose and Hawking are based on geodesic incompleteness. Physically, this criterion refers to the fate of classical test particles. What if one uses quantum fields instead? They would be more fundamental probes. For technical simplicity, I will restrict myself to cosmological singularities and show that one can unambiguously evolve quantum
fields across them in a...
I will discuss two complementary ways that one can address the quantum nature of radiation fields, with special reference to gravitational radiation. One, based on the Feynman-Vernon influence functional, is in principle complete, but challenging to work out fully. The second, based on minimal modeling of space-time and quantum theory, is extremely tractable, and sheds considerable light on...
Motivated in part by the recent measurements of the Borexino Collaboration, I will describe the current status of solar neutrino physics, including the impact of measurements on our knowledge of neutrino properties. Questions remain about the sun’s metallicity and the equivalence of its weak and electromagnetic luminosities — topics relevantly, respectively, to early solar evolution and to...
We discuss the emergence of black hole shadow and photon-sphere inthe context of f(R) gravity. It is shown that the shadow is exponentially sensitive to linear instabilities of metric coming from some f(R) solutions. Thus, the instabilities of photon circular trajectories, delimiting the black hole photon-sphere, are double exponentialized. Specifically we individuate two Lyapunov exponents,...
Study the cosmological sources at their cosmological rest-frames are crucial in order to track the cosmic history and properties of the compact objects. In view of increasing data volume of existing and upcoming telescopes/detectors we here apply the 1--dimensional convolutional neural network (CNN) to estimate the redshift of quasars in Sloan Digital Sky Survey IV (SDSS-IV) catalog from DR16...
I will review several GRB correlations reported in the literature and discuss possible physical mechanisms behind them. Topics to be covered include Amati/Yonetoku relations, Frail relation, Ghirlanda/Liang-Zhang relations, energy/luminosity-Lorentz factor (Liang-Lü relation), Dainotti relation, and several three-parameter fundamental-plane relations. These correlations provide hints on the...
The mid-frequency GW band (0.1-10 Hz) between LIGO-Virgo-KAGRA detection band and LISA-TAIJI-TIANQIN detection band is rich in GW sources. In addition to the intermediate BH (Black Hole) Binary coalescence (an event is detected by LIGO-Virgo collaboration recently), the inspiral phase of stellar-mass coalescence and GWs from compact binaries falling into intermediate BHs, it also enable us to...
Jets from super-massive-black-holes radiate photons over the whole electromagnetic spectrum, from the radio band up to TeV gamma-rays. Understanding the radiative mechanisms at work is a fundamental step for the study of particle acceleration in black-hole's jets, and to constrain jets structure, composition, and propagation. Using the information from multi-wavelength observations, several...
In this talk I will give a brief historical review of the original warp bubble geometry, as well as the main problems with it, namely the need for negative energy and the horizon problem.
The null-surface formulation (NSF) of general relativity is equivalent to standard general relativity but uses families of null surfaces rather than the metric or a connection. The NSF can be constructed in dimension 3+1, in any dimension higher, and also in dimension 2+1, which is a special case: In 2+1 dimensions, the main NSF field equation is equivalent to Cartan’s metricity condition. The...
In this talk, we shall present our recent studies on gravitational waves (GWs) produced by remote compact astrophysical sources. To describe such GWs properly, we introduce three scales, the typical wavelength of GWs, the scale of the cosmological perturbations, and the size of the observable universe. For GWs to be detected by the current and foreseeable detectors, we show that such GWs can...
After recent technological advancements in astronomical surveys, modern astrophysics is concerned with the study and characterization of distant objects such as galaxies, stars and quasars. Obtaining the optical spectrum and consequently deriving the redshift could instantly classify these astronomical sources but as long as spectroscopic observations are not available for many galaxies and...
The phenomena of standing waves is well known in mechanical and electromagnetic setting where the wave has the maximum and minimum amplitude at the antinodes and nodes, respectively. In the context of the exact solution to Einstein Field equations, we analyze a spacetime which represents standing gravitational waves in an expanding Universe. The study the motion of free masses subject to the...
During the early phase of in-spiral of a binary system, the tidal heating of a compact object due to its companion plays a significant role in the determination of the orbital evolution of the binary. The phenomenon depends crucially on the `hairs', as well as on the nature of the compact object. It turns out that the presence of extra dimension affects both these properties, by incorporating...
Both wormholes and warp drives, concepts originally developed within the context of science fiction, have now (for some 30 odd years) been studied and carefully analyzed within the framework of general relativity. An overarching theme of the general relativistic analysis is unavoidable violations of the classical energy conditions. Another science fiction trope, now over 80 years old, is the...
The observation of a very-high-energy neutrino by IceCube (IceCube-170922A) and its association with the flaring blazar TXS 0506+056 provided the first multimessenger observations of a blazar jet, demonstrating the important role of protons in their dynamics and emission. In this paper, we present SOPRANO, a new conservative implicit kinetic code which follows the time evolution of the...
The correlation between the photon energy at which the nuFnu spectrum in the cosmological rest-frame peaks, Ep,i, and the isotropic-equivalent radiated energy, Eiso, is one of the most investigated observaitonal properties of Gamma-Ray Bursts (GRB). In addition to its relevance for understanding the physics of prompt emission, identifying sub-classes of GRBs, shedding light on jet structure...
A significant number of stellar-mass black-hole (BH) binaries may merge in galactic nuclei or in the surrounding gas disks. With purposed space-borne gravitational-wave observatories, we may use such a binary as a signal carrier to probe modulations induced by a central supermassive BH (SMBH), which further allows us to place constraints on the SMBH's properties. We show in particular the de...
Searching continuous gravitational waves from unseen objects is computationally expensive and relies on hierarchies of follow-up stages for candidates above a given significance threshold. Clustering is a powerful technique that bunds together nearby candidates in a single follow-up to simplify the follow-ups and reduce the computational cost. We used deep learning methods to automate the...
We wish to investigate if we can extend the insights provided by the publication "Can stellar mass black holes be quark stars?" by Z. Kovacs,et.al. in MNRAS, 2009 as to answering their question via examining what may happen in a quark star - black hole binary in its Gravitational wave generation. In doing so, we also examine how to Use this idea to explore the idea of a black hole as a...
The properties of interior spacetimes sourced by stationary cylindrical anisotropic fluids are analytically studied for both nonrigid and rigid rotation. The gravito-electromagnetic features of different classes of such GR solutions are described. Their regularity conditions and those for their junction to a vacuum exterior are provided. A new class of rigidly rotating exact solutions to...
With the advent of NASA's Artemis program, ESA's European Large Logistic Lander, and China’s Chang’e mission, there is a growing impetus across funding agencies and private sectors for scientific payloads on the lunar surface. In this talk, I will review the ongoing efforts for Gravitational-Wave Lunar Observatory for Cosmology (GLOC) - the first concept design in the NASA Artemis era for a...
Blazars are a subclass of active galaxies with jets closely aligned to the observer's line of sight. In addition, they are the most powerful persistent sources across the electromagnetic spectrum in the universe. The detection of a high-energy neutrino from the flaring blazar TXS 0506+056 and the subsequent discovery of a neutrino excess from the same direction have naturally strengthened the...
Solitons in space–time capable of transporting time-like observers at superluminal speeds have long been tied to violations of the weak, strong, and dominant energy conditions of general relativity. This talk presents an approach to identify soliton solutions capable of superluminal travel that are sourced by purely positive energy densities. This is the first example of hyper-fast solitons...
The central engine of gamma-ray bursts may be neutron stars. However, the internal structure of neutron stars is still largely uncertain. It has been suggested that strange-quark matter (SQM) may be the true ground state of hadronic matter, indicating that the observed pulsars may actually be strange stars (SSs), but not neutron stars. According to the SQM hypothesis, the existence of a...
We construct from first principles the geometry of an analytic, exponentially localized five-dimensional brane-world black hole. The black-hole singularity lies entirely on the 3-brane, while the event horizon is shown to have a pancake shape. The induced line-element on the brane assumes the form of the Schwarzschild solution while the bulk geometry is effectively AdS$_5$ outside the horizon....
Along with the accumulated cosmological observations, while the standard paradigm of modern cosmology has been verified with high precision, some new challenges such as the $H_0$ tension appear. To address these issues, we in this article reconstruct the free function of $f(T)$ gravity in a model-independent manner using the combined observational data. The obtained function is consistent with...
Abstract.
We discuss the possibility that the topological structure of the Universe may possess fractal properties.
Relic wormholes and their fractal distribution are predicted in a natural way by lattice quantum gravity models.
This gives a new approach to some long-standing problems. Those are the nature of dark matter phenomena, the origin of Faber-Jackson and Tully-Fisher...
Gravitational waves excite quadrupolar vibrations of elastic bodies. Monitoring these vibrations was one of the first concepts proposed for the detection of gravitational waves by Joseph Weber. At laboratory scale, these experiments became known as resonant-bar detectors, which form an important part of the history of GW detection. Due to the dimensions of these bars, the targeted signal...
The progenitors of high-energy (HE) neutrinos detected by the IceCube observatory (> 30 TeV) remain on the discussion. Astrophysical events such as Gamma-ray bursts (GRBs), Supernova remnants (SNR), Tidal disruption events, and Active galactic nuclei (AGN) are proposed as HE neutrinos progenitors. So far, the only detection in space-time coincidence with a neutrino event is by the TXS...
Alcubierre warp drive spacetimes allow timelike observers to travel superluminally relative to other timelike observers through the use of negative energy densities. In our study, we develop a general framework for describing warp drives. We show that any such object may be thought of as a shell of inertially moving material that modifies the properties of spacetime enclosed by the shell....
Recently, very high-energy photons above 100 GeV were reported to be detected from GRB 190114C and GRB 180720B at, respectively, 100–1000 s and 10 hr after the burst. We model the available broadband data of both GRBs with the synchrotron plus synchrotron self-Compton (SSC) emission of the afterglow shocks. We find that the sub-TeV emission of GRB180720B can be interpreted as the SSC emission...
We reduplicate the Book “Dark Energy” by M. Li, X-D. Li, and Y. Wang, zero-point energy calculation with an unexpected “length’ added to the ‘width’ of a graviton wavefunction just prior to the entrance of ‘gravitons’ to a small region of space-time prior to a nonsingular start to the universe. We compare this to a solution worked out using Klauder Enhanced quantization, for the same given...
Recent progresses in Machine Learning have unlocked new possibilities to tackle scientific problems by means of neural networks, and already many applications have been developed both in astrophysics and cosmology. In this presentation, using a Generative Adversarial Network (GAN), an unsupervised learning model, we demonstrate the possibility to learn the distribution of dark matter of the...
Understanding gravitational wave memory effects for exact radiative solutions in General Relativity (GR) have received considerable attention lately, following the work of Zhang, Duval, Gibbons and Horvathy (PRD, 2017). In principle, one can arrive at these effects by studying the separation of pairs of geodesics in such spacetimes. Radiative geometries such as Kundt waves have shown to...
The Lunar Gravitational-Wave Antenna (LGWA) is a proposed low-frequency gravitational-wave detector on the Moon’s surface.
Its core will be composed of an array of high-end seismic sensors: CSIS (Cryogenic Superconducting Inertial Sensor).
A cryogenic environment will be used in combination with superconducting materials to open up pathways to low-loss actuators and sensor mechanics.
CSIS...
This is the fourth paper of a series where we examine solutions of the Einstein equations with the Alcubierre warp drive geometry having different matter and field sources (Santos-Pereira et al. 2020, 2021; Refs. [1–3]). The Alcubierre metric describes a spacetime geometry that allows a massive particle inside a spacetime distortion, called warp bubble, to travel with superluminal global...
Since its discovery in 2005, the plateau phase seen in the early x-ray afterglow of a significant fraction (10's of %) of GRBs confuse theoreticians. A close look reveals that "plateau" bursts nearly never show evidence for LAT emission, neither a thermal component. Using this a hint, I argue that the plateau is due to the coasting of GRB jets in a "wind"-like medius. I will provide the...
Two major challenges in modern cosmology are the understanding of the origin and growth of cosmic structure and the progenitors of Gravitational Waves. Both scenarios require heavy computational resources to perform simulations and inference. In this work, we propose to adopt Machine Learning to alleviate these requirements, to enable significantly faster sampling and inference. We show that...
Gravitational-wave (GW) memory effects are lasting changes in the GW strain and its time integrals following bursts of GWs. They are closely related to the symmetries of asymptotically flat spacetimes and their corresponding conserved charges. There are three types of GW memory effects (displacement, spin, and center-of-mass) that are related to different conserved charges and have different...
We utilize radio interferometric (VLBI) observations to tackle the problem of determining high-energy neutrino origins. Specifically, we find blazars positionally associated with IceCube neutrino detections to exhibit stronger parsec-scale radio emission compared to the rest of the sample. The probability of a chance coincidence is only 4*10^-5 (4.1 sigma). There are at least 70 bright blazars...
Using the algorithm proposed to map solutions of General Relativity (GR) into Ricci-Based Gravity theories, we extend the search for scalar configurations in quadratic gravity theories with curvature dependence in both Ricci scalar, $R$, and Ricci-squared scalar, $Q=R_{\mu\nu}R^{\mu\nu}$. We describe the general method to map a scalar configuration of GR into $f(R,Q)$, and illustrate this...
TOBA (TOrsion-Bar Antenna) is a mid.-frequency gravitational-wave antenna. It is formed by two bar-shape test masses, each suspended as a torsion pendulum. Tidal effect originated by incoming gravitational wave will be detected as differential angular motion of these two bars. The fundamental sensitivity is 10^(-19) Hz^(-1/2) at 0.1 Hz frequency band, assuming 10-m scale cryogenic detector....
In this work we study the problem of linear stability of gravitational perturbations in stationary and spherically symmetric wormholes. For this purpose, we employ the Newman-Penrose formalism which is well-suited for treating gravitational radiation in General Relativity, as well as the geometrical aspect of this theory. With this method we obtain a "master equation" that describes the...
We investigate a family of ultra-static, Lorentzian wormholes for which the wormhole shapes and sizes are controlled by two metric parameters –b_0 (the throat radius) and n (an even integer). The well-known Ellis- Bronnikov wormhole is a special case (n= 2) in this family. The n>2 spacetimes are however, distinctly different geometrically, a fact evident from their embedding...
The Fermi blazar observations show a strong correlation between $\gamma$-ray luminosities and spectral indices. BL Lac objects are less luminous with harder spectra than flat-spectrum radio quasars (FSRQs). Interestingly FSRQs are evident to exhibit a Keplerian disc component along with a powerful jet. We compute the intrinsic jet luminosities by beaming corrections determined by different...
We discuss the status of observables and operator ordering ambiguities in the quantum cosmology model with Brown Kuchař dust as the matter field. In order to study the dynamics of the FRW universe, Hubble parameter and Ricci scalar are expressed as a function of phase space variables. As these functions exhibit operator ordering ambiguity, several Hermitian extensions corresponding to these...
The Zhaoshan long-baseline Atom Interferometer Gravitation Antenna (ZAIGA) is a proposed underground long-baseline atom interferometer facility, aiming for experimental research on gravitation and related problems. It will be equipped with long-baseline atom interferometers, high-precision atom clocks, and large-scale gyros. ZAIGA facility will take an equilateral triangle configuration with...
The origin of the plateau phase seen in the early X-ray light curves of GRBs (up to thousands of seconds) is a debated topic. I will present a new model formulation as explanation of the plateau emission and its application to the observation in both X-ray and optical bands. Main outcomes of this application is that (i) the end of the plateau phase marks the transition from the coasting phase...
Galaxy Clusters are essential to study galaxy evolution and sensitive probes of cosmology and the dynamics of the Universe Dark sector. Large galaxy surveys, such as Euclid, DES, LSST/Rubin will provide a wealth of information that can be used to detect many new clusters. For example, the Euclid mission survey may reveal more than 60000 clusters with S/N>3 up to redshift 2, representing a...
We study the absorption of massless scalar waves in a geometry that interpolates between the Schwarzschild solution and a wormhole that belongs to the Morris-Thorne class of solutions. In the middle of the interpolation branch, this geometry describes a regular black hole. We use the partial wave approach to compute the scalar absorption cross section in this geometry. Our results show that...
For gamma-ray bursts (GRBs) with a plateau phase in the X-ray afterglow, a so-called L-T-E correlation has been found which tightly connects the isotropic energy of the prompt GRB (Eγ,iso) with the end time of the X-ray plateau (Ta) and the corresponding X-ray luminosity at the end time (LX ). Here we show that there is a clear redshift evolution in the correlation. Furthermore, since the...
I will discuss prospects for GW detection with AION and AEDGE, atom interferometry experiments focusing on the mid-frequency band.
The BL Lacs Mrk 421 and Mrk 501 show fast variability in the TeV-band flares, indicating a compact emission region. The lack of correlation between X-ray and TeV flux hints at more than one emission zone. Both sources have shown temporary extreme behavior. In this work, we used a lepto-hadronic model with two-zone emission to explain the spectral energy distribution during the very...
We generate two anisotropic solutions for a static sphere filled with quark matter in the framework of self-interacting Brans-Dicke theory. For this purpose, we add an anisotropic source in the seed distribution and decouple the field equations through deformation in the radial metric function. As a result of this transformation, the field equations are disintegrated into two systems which...
The fourth Fermi Large Area Telescope source catalog contains 5065 gamma-ray sources. Among these sources, 694 are flat-spectrum radio quasars (FSRQs), 1131 are BL Lac-type objects (BL Lacs), and 1312 are blazar candidates of an unknown type (BCUs). Using as a training sample the spectral energy distributions and the light curves of classified blazars, a supervised machine learning method...
The classical singularity theorems of General Relativity rely on energy conditions that are easily violated by quantum fields. In this talk I will provide motivation for an energy condition obeyed by semiclassical gravity: the smeared null energy condition (SNEC), a proposed bound on the weighted average of the null energy along a finite portion of a null geodesic. I will then then present the...
We propose a Backscattering dominated prompt emission model for gamma ray bursts' (GRB) prompt phase in which the photons generated through pair annihilation at the centre of a GRB are backscattered through Compton scattering by an outflowing stellar cork. Using pair annihilation spectrum for seed photons, we show that the obtained spectra are capable of explaining the low energy and the high...
We utilize how Weber in 1961 initiated the process of quantization of early universe fields to the problem of what may be emitted at the mouth of a wormhole. While the wormhole models are well developed, there is as of yet no consensus as to how, say GW or other signals from a wormhole mouth could be quantized, or made to be in adherence to a procedure Weber cribbed from Feynman, in 1961.
In...
High-redshift blazars are among the most powerful objects in the Universe. The spectral and temporal properties of 33 distant blazars (z > 2.5) detected in the high-energy gamma-ray band will be discussed using the Fermi-LAT and Swift Ultraviolet and Optical Telescope/X-ray Telescope (UVOT/XRT) data accumulated during 2008-2018. The properties of those blazar jets obtained by modeling the...
DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a future Japanese space gravitational-wave antenna. There are many science targets that DECIGO aims at, including the detection of primordial gravitational waves, direct measurement of the acceleration of the Universe, the revelation of the formation of massive black holes, and many others. DECIGO consists of four clusters of...
Gamma-ray bursts (GRBs) correspond to the most energetic electromagnetic events known. These events can release a large amount of energy during a time scale ranging from a few milliseconds to tens of seconds. Based on their duration, we can classify them into short and long events, being the production process in each case different. In this work, we study this sort of astrophysical source...
In this talk the geometrical methods and symmetry principles in gravitation are explored motivating a new perspective into the spacetime paradigm. The effects of post-Riemann spacetime geometries with torsion are briefly studied in applications to fundamental fermionic and bosonic fields, cosmology, astrophysics and gravitational waves. The physical implications and related phenomenological...
After more than 14 years activity, the AGILE satellite continues its exploration of the high-energy sky, investigating galactic and extragalactic sources in the hard X- and gamma-ray energy range. Among its scientific targets, Gamma-Ray Bursts (GRBs) represent one of the most interesting topics. In particular, the AGILE minicalorimeter (MCAL; 0.4-100 MeV) offers the opportunity to detect GRBs...
Borexino, a large volume detector for low energy neutrino spectroscopy, is currently taking data underground since 2007 at the Laboratori Nazionali del Gran Sasso, Italy. The main goal of the experiment is the real-time measurement of solar neutrinos, especially the low energy part of the spectrum. Neutrinos are detected via neutrino-electron scattering in an ultra-pure organic liquid...
We consider the possible existence of gravitationally bound stringlike objects in the framework of the generalized hybrid metric-Palatini gravity theory, in which the gravitational action is represented by an arbitrary function of the Ricci and of the Palatini scalars, respectively. The theory admits an equivalent scalar-tensor representation in terms of two independent scalar fields. Assuming...
Photons emitted by light sources in the neighbourhood of a black hole can wind several times around it before fleeing towards the observer. For spherically symmetric black holes, two infinite sequences of images are created for any given source, asymptotically approaching the shadow border with decreasing magnitude. These sequences are reflected by a characteristic staircase structure in the...
Intrinsic Gravitational Modes (IGM) involving electromagnetic field fluctuations are found that are sustained by the time-dependent tridimensional gravitational field of Black Hole binaries when their collapse is approached. These “disk-rippling” modes, emerging from a plasma disk structure surrounding a binary, have ballooning amplitude profiles in the "vertical" direction (referring to the...
We study the entanglement production for Dirac and Klein-Gordon fields in an expanding spacetime characterized by the presence of torsion. Torsion is here considered according to the Einstein-Cartan theory with a conformally flat Friedmann-Robertson-Walker spacetime. In this framework, torsion is seen as an external field, fulfilling precise constraints directly got from the...
Rotational irregularities in neutron stars, principally glitches and timing noise, are often regarded as nuisance phenomena which are subtracted from electromagnetic pulsar timing data in order to reveal the underlying, secular rotational evolution. This represents a missed opportunity. Glitches and timing noise excite internal degrees of freedom in the star impulsively and stochastically. The...
In the talk, I review a string-inspired running vacuum model (RVM) of Cosmology, and its potential connection with the dark sector of the (observable) Universe. Specifically, I consider a gravitational model of the early Universe that is inspired by the low-energy effective actions of string theory. I assume that only gravitational degrees of freedom appear as external fields at early eras. I...
At last, in few months, the window of Astronomical X-ray polarimetry will be re-opened after more than 40 years. IXPE the Imaging X-ray Polarimetry Explorer, is the next NASA Small Explorer Mission with a decisive contribution of Italy. Three X-ray mirrors focalize the radiation into three detector units that host the polarization sensitive detectors entirely devised, built, tested and...
We will discuss Mirror dark matter searches from
Direct detection underground experiments, ultra cold neutrons and gravitational waves physics.
It is reasonable to think that the spin labels of spin networks have nothing to do with physical rotation or spin. However, intriguingly, in situations involving rotating black holes, a connection between the spin of spin networks and angular momentum has been established. Here I want to consider this connection from another angle: Can we talk about the spin of fermions in loop quantum...
The dual phase Time Projection Chamber detectors exploiting Xenon element is the leading technology in the field of direct Dark Matter searches, as testified by the most stringent upper Limit on WIMP-nucleon cross section set by the XENON1T experiment. The XENONnT experiment, currently, under commissioning at the Gran Sasso underground laboratories, is ready to start its physics program. It...
We are using the book “Towards Quantum Gravity with an article by Claus Kiefer as to a quantum gravity interpretation of the density matrix in the early universe. The density matrix we are using is a one loop approximation, with inflaton value and potential terms, like V(phi) using the Padmanabhan values one can expect if the scale factor is a ~ a(Initial) times t ^ gamma , from early times ....
Recently there has been a surge of interest in regularizing a $ D \to 4 $ limit of, the Einstein-Gauss-Bonnet (EGB) gravity, and the resulting regularized $4D$ EGB gravity has nontrivial dynamics. The theory admits spherically symmetric black holes generalizing the Schwarzschild black holes. Furthermore, the $4D$ non-relativistic Horava-Lifshitz theory of gravity also admits the identical...
The enhanced X-ray Timing and Polarimetry Mission -- eXTP is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism.
Primary targets include stellar-mass and supermassive black holes, isolated and binary neutron stars, and strong magnetic field systems like magnetars.
In addition to investigating fundamental physics, eXTP will be...
In this talk, I will review the current status of the timing of PSR J2222-0137, which promises to be one of the most important laboratories for testing the nature of gravitational waves, for limiting the variation of Newton's gravitational constant, and for testing non-perturbative deviations from general relativity in the behavior of gravity (in particular the phenomenon of ``spontaneous...
Thanks to the CLASH and Frontier Fields (FF) programs of the Hubble Space Telescope, it has been possible to identify an unprecedented number of strongly lensed sources in the central regions of several galaxy clusters. Complementing these observations with MUSE spectroscopy, we obtain high fidelity mass models for MACSJ1206, MACSJ0416, and AS1063. The models are consistent with the presence...
We implement Polymer Quantum Mechanics on the Hamiltonian formulation of the isotropic Universe in both the representations of the standard Ashtekar-Barbero-Immirzi connection and of a new generalized coordinate conjugate to the Universe volume. The resulting morphology is a bouncing cosmology; when quantizing the volume-like variable the Big Bounce is an intrinsic cut-off on the cosmological...
The eXTP (enhanced X-ray Timing and Polarimetry) mission is a flagship international collaboration mission led by China, with large contribution from European countries. The eXTP mission is designed to study the equation of state of ultra-dense matter under extreme conditions of strong gravity, density and magnetic field. Its primary targets contain the isolated and binary neutron stars,...
Geometric optics and its corrections are typically derived using a high-frequency WKB ansatz, which results in a tower of transport equations along null geodesics. Separately, field propagation can be described using Green functions, which are known to have a Hadamard form involving certain bitensors. In this talk, it will be explained how these two perspectives on field propagation complement...
We explore a geometrical mechanism of cancellation that heals the cosmological constant problem. To do so, during the primordial universe we assume quantum fluctuations to hold and the effective cosmological constant built up in terms of its bare and quantum contributions. We thus notice that if we assume a discontinuity of the Friedmann-Robertson-Walker metric, a corresponding phase of energy...
There has been observational evidence about spin axes of quasars in large quasar groups correlated over hundreds of Mpc. This is seen in the radio spectrum as well as in the optical range. There is not yet a satisfactory explanation of this "spooky" alignment.
This alignment cannot be explained by mutual interaction at the time that quasars manifest themselves optically. A cosmological...
Timing noise in a pulsar is the stochastic deviation of the pulse arrival times of the pulsar away from its long term spin down trend. In the classic two-component neutron star model, interactions between the crust and superfluid cause these perturbations to decay exponentially with a characteristic timescale. This research uses a Kalman filter to track the pulsar frequency through time and to...
The Fermi Gamma-ray Space Telescope has provided unique insights into the Universe’s biggest explosions over the past 13 years. With thousands of gamma-ray bursts (GRBs) detected by the Gamma-ray Burst Monitor (GBM) and hundreds by the Large Area Telescope (LAT), we have studied the properties of the populations of these events and obtained unique insights into their emission mechanisms,...
The discordance can be due to a wide range of non-standard cosmological or astrophysical processes as well as from some particular systematics. Here, without considering any particular astrophysical process or extension to the standard model at the background level, we look to project the effect of these differences in the values of the key cosmological parameters on to the shape of the...
In this talk I will present a class of direct detection signals; absorption of fermionic dark matter. I enumerate the operators through dimension six which lead to fermionic absorption, study their direct detection prospects, and summarize additional constraints on their suppression scale. Such dark matter is inherently unstable as there is no symmetry which prevents dark matter decays....
Theories of Quantum Gravity predict a minimum measurable length and a corresponding modification of the Heisenberg Uncertainty Principle to the so-called Generalized Uncertainty Principle (GUP). However, this modification is non-relativistic, making it unclear whether the minimum length is Lorentz invariant. We formulate a Relativistic Generalized Uncertainty Principle, resulting in a Lorentz...
Despite over 50 years of Gamma-Ray Burst (GRB) observations many open questions remain about their nature and the environments in which the emission takes place. Polarization measurements of the GRB prompt emission have long been theorized to be able to answer most of these questions. The POLAR detector was a dedicated GRB polarimeter developed by a Swiss, Chinese and Polish collaboration. The...
We provide an update on the ongoing monitoring and study of the highly-relativistic double neutron star binary system, PSR J1757-1854, a 21.5-ms pulsar in a highly eccentric, 4.4-hour orbit. The extreme nature of this pulsar’s orbit allows it to probe a parameter space largely unexplored by other relativistic binary pulsars. For example, it displays one of the highest gravitational wave (GW)...
The nonprojectable version of the Horava theory has a dynamics closer to general relativity than the projectable case, since it possesses the so-called Hamiltonian constraint. But the nonprojectable version is a field theory with second-class constraints, the Hamiltonian constraint being one of them. This feature poses challenges in understanding its quantization. The main unanswered question...
About 99 percent of solar energy is produced through sequences of nuclear processes that convert hydrogen into helium in the so-called pp-chain. The neutrinos emitted in five of these reactions represent a unique probe of the Sun’s internal working and, at the same time, offer an intense natural neutrino beam for fundamental physics research.
The Borexino experiment consists of a large-volume...
The nature of dark matter is expected to be most strongly expressed in dark matter subhaloes with mass $<10^{9}\mathrm{M}_{\odot}$. These subhaloes are accessible to us in the vicinity of the Milky Way (MW), through the abundance and structure of both luminous MW satellites and dark subhaloes that never form stars. In this talk I will present work on the properties of these subhaloes in two...
Loop quantum gravity (LQG) in its current formulation is a the quantisation of the SU(2) gauge theory of gravity in Ashtekar-Barbero variables. It started out as an SL(2,C) gauge theory in Ashtekar's selfdual variables, but the quantisation program was never fully carried out in this formulation. The two main obstacles are the non-compactness of the gauge group SL(2,C) and the necessity to...
I will present the latest results on our analysis of the non-linear X-ray to ultraviolet luminosity relation in a sample of optically selected quasars from SDSS, cross-matched with the most recent XMM-Newton and Chandra catalogues. I will show that this correlation is very tight, implying that the observed relation is the manifestation of an ubiquitous (but still unknown) physical mechanism,...
It is argued that the past of the Universe, extrapolated from standard physics and measured cosmological parameters, might be a non-singular bounce without any exotic hypothesis. We show that, in this framework, stringent constraints can be put on the reheating temperature and number of inflationary e-folds. We draw some conclusions about the shape of the inflaton potential and raise the...
The DAMA/LIBRA experiment shows $9.5 \sigma$ evidence for an annual modulation in the $(1-6)~ {\rm keV}$ energy range, strongly suggesting that the observed modulation has the dark matter origin. However, the conventional interpretation in terms of WIMP-nucleon interaction is excluded by other experiments. We propose an alternative source of modulation based on the so-called axion...
We investigate the properties of anisotropic, spherically symmetric compact stars, especially neutron stars and strange quark stars, made of strongly magnetized matter. The neutron stars are described by a polytropic equation of state, the strange quark stars by an equation of state based on the MIT Bag model. The stellar models are based on an a priori assumed density dependence of the...
The GRAVITY instrument at the Very Large Telescope (VLT) has transformed the Galactic centre into a laboratory to test the strong field regime of gravity theories. The supermassive black hole in the center of the Milky Way (Sgr A*) is, at a distance of 8kpc, the closest of its kind and the largest in the sky. It is surrounded by a nuclear cluster of high velocity stars called S-stars, whose...
This talk will provide an overview of our current knowledge and understanding of high energy (~0.1-100 GeV) emission from GRBs. Potentially relevant emission mechanisms will be discussed along with what we have learned from existing observations, most notably by Fermi, which has greatly contributed to our knowledge of GRB physics as well as in other areas. Fermi high-energy prompt GRB...
After more than a century of modern cosmology in which model assumptions were indispensable to interpret the sparse and vague data, we are finally able to replace model assumptions by observational evidence. With telescopes like Hubble, the development of adaptive optics for ground-based facilities, and installations of integrated field units, the amount of high-quality data has vastly...
We present an overview of a search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1 (Sco X-1), using two pipelines: a hidden Markov model (HMM) and a cross correlation approach. This search improves on previous Sco X-1 searches by introducing new features for each pipeline. For the HMM model, we use a new frequency domain matched filter. The cross correlation...
The enhanced X-ray Timing and Polarimetry mission (eXTP) is a flagship observatory for X-ray timing, spectroscopy and polarimetry developed by an International Consortium led by the Chinese Academy of Science, with a large participation of European institutions.
Thanks to its very large collecting area, good spectral resolution and unprecedented polarimetry capabilities, eXTP will explore the...
Existence of the Dark Energy became now a commonly-accepted paradigm of cosmology, but the physical essence of this quantity remains absolutely unknown and its numerical values are drastically different in the early and modern Universe. In fact, the Dark Energy is usually introduced in literature either by postulating some additional terms in the Lagrangians or by employing the empirical...
The standard Lambda CDM cosmological model now seems to face some puzzles. One of the most serious problems is the so-called Hubble tension; the values of the Hubble constant obtained by local measurements look inconsistent with that inferred from CMB. Although introducing extra energy components such as the extra radiation or early dark energy appears to be promising, such extra components...
We develop the various solutions of Einstein-Aether theory of gravity through reconstruction approach. In order to discuss the current cosmic acceleration corresponding to our reconstructed models, we evaluate different cosmological parameters. Also, we also discuss the consistency of our results of cosmological parameters with current observational data for ensuring the viability of models.
Gamma-ray bursts are among the most luminous transients in the Universe, a characteristic that permits us to observe them at very high redshifts. For this reason, many efforts have been made to identify a method to use GRBs as cosmological distance indicators through the use of luminosity correlations between their high-energy observable quantities. In this talk, I will review some of the most...
There is a robust signal for a 511 keV photon line from the galactic center which may originate from dark matter particles with masses of a few MeV. I will introduce a model in which dark matter first decays into a pair of intermediate pico-charged particles CC¯ with a lifetime much larger than the age of the universe. The galactic magnetic field accumulates the relativistic CC¯ that...
Many quantum gravity theories predict several interesting phenomenological features such as minimal length scales and maximal momenta. Generalized uncertainty principles (GUPs), which are extensions of the standard Heisenberg uncertainty principle, have proven very useful in modelling the effects of such features on physics at sub-Planck energy scales. In this talk, we use a GUP modelling...
Modern astronomy has entered the multi-wavelength and multi-messenger era, and time-domain astronomy is one of the leading frontiers. Around 2030, a series of all-sky monitors and survey missions will discovery more than tens of thousands of transients every day. However, the existing and planned telescopes can not simultaneously perform follow-up observations for so many transients of...
Timing relativistic binary pulsar systems have enabled the measurements of precise neutron star masses and fundamental tests of gravity in the strong field regime. The measurement of neutron star masses not only provide insight into the elusive neutron star interior, but also help constrain binary evolution theories and supernova physics. For many binary systems in the southern hemisphere, the...
Solar neutrinos provide a sample of electron neutrinos of different energies. They are therefore a unique probe of the electron neutrino propagation through solar matter and for the experimental study of the MSW effect. Borexino, with its unique purity and sensitivity, has been able to study individually all components, extracting the best test of electron neutrino survival probability to...
Fuzzy Dark Matter (FDM), consisting of ultralight bosons ($m_{\rm b} \sim 10^{-22} \rm eV$), is an intriguing alternative to Cold Dark Matter. Numerical simulations that solve the Schrodinger-Poisson (SP) equation show that FDM halos consist of a central solitonic core, which is the ground state of the SP equation, surrounded by an envelope of interfering excited states. These excited states...
Ground-based gravitational-wave detectors are becoming more sensitive, and in the near future we hope to detect a gravitational-wave background. However, as these detectors become more sensitive they will continue to run into new forms of noise. Correlated noise between spatially separated detectors will limit our intrinsic sensitivity, and have the potential to give a false detection. In this...
There is a small sample of long-duration gamma-ray bursts built on the intersection of two types of events: bursts associated with supernovae (GRB-SN) and bursts emitting high-energy photons (GeV-GRB). Being only few cases these GeV-GRB-SN can nevertheless shed some light on the emission mechanisms spanning the whole electromagnetic spectrum. We systematize the known events and analyze the new...
Neutron stars (NSs) harbour extremely powerful magnetic fields, leading to their shape being deformed. The magnetic deformation of NSs depends both on the geometry - and strength - of their internal magnetic field and on their composition, encoded by the equation of state (EoS). However, both the details of the internal magnetic structure and the EoS of the innermost part of NSs are mostly...
This talk is devoted to the quantization of supergravity in a formulation in which (part of) supersymmetry manifests itself in terms of a gauge symmetry. Applications we have in mind are supersymmetric black holes and loop quantum cosmology.
We will derive the Holst variant of the MacDowell-Mansouri action for $\mathcal{N}=1$ and $\mathcal{N}=2$ supergravity in $D=4$ for arbitrary...
Each and every observational information we obtain from the sky regarding the brightnesses, distances or image distortions resides on the deviation of a null geodesic bundle. In this talk, we will present the symplectic evolution of it on a reduced phase space. The resulting formalism is analogous to the one in paraxial Newtonian optics. It allows one to identify any spacetime as an optical...
Primary science goals for the Enhanced X-ray Timing and Polarimetry (eXTP) mission include studies of matter under conditions of extreme density and strong gravity. I will describe how eXTP's observations of neutron stars and black holes will lead to major advances in both of these areas.
Exploring the effects of geometry, topology, dimensionality, and interactions on ultracold atomic ensembles has proven to be a continually fruitful line of inquiry. One heretofore unexplored configuration for such ensembles is that of a bubble or shell, where trapped atoms are confined in the vicinity of a spherical or ellipsoidal surface. Such a system could offer new collective modes,...
I will explain the limitations of resolutions to Hubble tension within Einstein gravity and the FLRW paradigm. I will then leverage persistent discrepancies in the cosmic radio dipole to argue that we must move beyond FLRW. I will provide hints across various cosmological probes that the Hubble constant is higher in the hemisphere aligned with the CMB dipole.
Boundary conditions have physical consequences. On Lifshitz spacetimes, the Klein-Gordon equation gives rise to an initial-boundary value problem. This means that for a given suitable initial data, corresponding solutions might not exist. If they exist, then each boundary condition selects a different solution, thus yielding inequivalent dynamics. In this talk I will show that there is a...
Observations of the 21 cm signal through intensity mapping techniques are expected in the near future. This new observable will allow to probe evolution of the Universe in a very wide redshift range, from the dark ages, through the epoch of reionization up to the present time. We constrain cosmological parameters from forecast measurements of the 21 cm signal power spectrum $P_{21}(k,z)$...
Leptophilic dark matter (LDM) could naturally arise in many beyond the Standard Model scenarios and could address certain experimental anomalies. We will discuss some model-independent collider constraints on the LDM effective couplings with the Standard Model sector, considering its production at a future electron-positron linear collider (with polarized and unpolarized beam options) in the...
E. Virgilli, F. Frontera, P. Rosati, E. Caroli, L. Ferro, M. Moita, C. Labanti, R. Campana, F. Fuschino on behalf of a large collaboration
Gamma-ray astronomy is a branch whose potential has not yet been fully exploited. The observations of elemental and isotopic abundances in supernova (SN) explosions are key probes not only of the stellar structure and evolution but also for understanding...
Mass measurements of binary pulsars have provided significant constraints to the equation of state (EOS) of ultra-dense matter. The measurement of the moment of inertia (MOI) of a binary pulsar, however, would provide important additional constraints. The Double Pulsar, PSR J0737-3039A/B, is the most promising system for the first robust MOI measurement via high-precision pulsar timing. In...
We perform accurate relativistic atomic many-body calculations of the effects of dark matter produced in underground laboratories. Our recent calculation of the ionization of atoms by absorption of scalar particles gives cross section, which is several orders of magnitude smaller than that calculated by other authors. The reason is that the traditional plain wave approximation for outgoing...
The Fermi LAT spectra of many bright gamma-ray bursts have a power law component that extends to several GeV. This power law component is distinct from the Band function present at lower energies (< 10 MeV), and it suggests the importance of inverse Compton scatterings at high energies.
With the advent of GRB observations at very high energies by Imaging Atmospheric Cherenkov Telescopes...
We study Quantum Gravity effects on the density of states in statistical mechanics and its implications for the critical temperature of a Bose Einstein Condensate and fraction of bosons in its ground state. We also study the effects of compact extra dimensions on the critical temperature and the fraction. We consider both neutral and charged bosons in the study and show that the effects may...
Stars are fueled by nuclear reactions occurring in their core. In massive stars (approximately 1.3 more massive than our Sun) the dominant reactions are believed to be those belonging to the so-called CNO cycle, while in lighter stars (including our Sun) the proton-proton chain prevails. Until now, we had no direct experimental evidence of the existence of the CNO cycle.
Recently, the...
I will outline the so-called two-families scenario in which neutron stars (composed also of hadronic resonances and of hyperons) exist together with strange quark stars, i.e. compact objects composed entirely of deconfined quark matter. The two-families scenario has rather precise and explicit predictions concerning masses and radii, which can be tested by eXTP. In particular we predict the...
The occurence of infinite center of mass energies in particle collisions close to the horizon of an extremal Kerr black hole was first presented by Banados, Silk and West (BSW) in 2009. For their scenario, the rotation and the extremality of the black hole are key factors. Since their seminal paper, this phenomenon was studied for a large variety of spacetimes and for different particle...
Gravitational waves from the late inspiral, merger, and post-merger of a binary neutron star coalescence provide complementary information about the cold and hot equations of state of neutron star matter. These signals dominate in the kHz range, higher than the most sensitive part of the current generation of gravitational-wave interferometers. I will present the design concept and science...
Explaining the accelerated expansion of the Universe is one of the most challenging topic in physics today. Cosmography provides information about the evolution of the universe, assuming only that the space time geometry is described by the Friedman-Lemaitre-Robertson-Walker metric.Cosmography traditionally involves Taylor expansions of the observable quantities, and the results of this...
In this work, we study 5-dimensional braneworld scenarios in the scalar-tensor representation of the generalized hybrid metric-Palatini gravitational theory. We start by considering a model for a brane supported purely by the gravitational scalar fields of the theory and then consider other distinct cases where the models are also supported by an additional matter scalar field. We investigate...
I will discuss a new method of determining the spacetime curvature and matter density along the line of sight using variations of times of arrival (TOA) of electromagnetic signals, measured in the vicinity of two given points. We measure the variations of the TOA's up to quadratic order in the displacements of the source and the receiver with the help two groups of synchronised clocks,...
We study Brans-Dicke gravity with a cosmological constant and cold dark matter (BD-$\Lambda$CDM hereafter). This theory is the first historical attempt to extend Einstein's General Relativity by promoting the Newtonian coupling constant $G_N$ to a dynamical one $G(t)$. We present the background and the perturbation equations, which allows us to test the theoretical predictions with a complete...
We present a comparative analysis of current observational constraints on three recently discussed alternative models for explaining the low-redshift acceleration of the universe: the generalized coupling model by Feng and Carloni, the scale invariant model by Maeder (an example of a broader class first proposed by Canuto et al., which we also study), and the so-called steady-state torsion...
Given the Loop-Quantum-Gravity (LQG) non-graph-changing Hamiltonian $\widehat{H[N]}$, the coherent state expectation value $\langle\widehat{H[N]}\rangle$ admits an semiclassical expansion in $\ell^2_{\rm p}$. In this paper, we compute explicitly the expansion of $\langle\widehat{H[N]}\rangle$ on the cubic graph to the linear order in $\ell^2_{\rm p}$, when the coherent state is peaked at the...
Quantum Key Distribution (QKD) is essential for providing secure communication. For long distances QKD from space turns out to be most efficient. In this contribution the influence of general relativistic effects as well as of instrumental choices on secure QKD is analyzed. One aspects of the resut is that certain classes of orbits are not optimal for QKD. On the other hand, such orbits may be...
We study non-rotating and isotropic strange quark stars in Lorentz-violating theories of gravity, and in particular in Hořava gravity and Einstein-æther theory. For quark matter we adopt both linear and non-linear equations-of-state, corresponding to the MIT bag model and color flavor locked state, respectively. The new structure equations describing hydrostatic equilibrium generalize the...
We discuss the nature of phase transitions in the self-gravitating Fermi gas in Newtonian gravity and general relativity. When the particle number is above the Oppenheimer-Volkoff limit, we evidence the existence of a new turning point of mass-energy in the caloric curve leading to the collapse of the system towards a black hole. We mention possible applications of these results to the case of...
Strongly magnetized high energy astrophysical objects, including a variety
of pulsars and magnetars, are expected to produce high degree of X-ray
polarization, which can be used to diagnose the magnetic field, emission
mechanism, and geometry of the objects, and also test the fundamental
physics. In this talk, I will present possible science cases that the
enhanced X-ray Timing and...
From the assumption that the slow roll parameter
ε has a Lorentzian form as a function of the e-folds number N, a successful model of a quintessential inflation is obtained. The form corresponds
to the vacuum energy both in the inflationary and in the
dark energy epochs and satisfies the condition to climb from
small values of ε to 1 at the end of the inflationary epoch.
We find the...
Gamma-ray Bursts (GRBs) have always been considered within the highest priority targets for all modern imaging atmospheric Cherenkov telescopes (IACTs). For a long time, the detection of such events in the very-high-energy band (VHE; E>100 GeV) posed a major challenge for IACTs from both the technical and the scientific point of view. On the other hand, it was well proven that the possibility...
The surface brightness fluctuations (SBF) method is one of the most robust extragalactic distance indicators: with an accuracy comparable to SNe Ia and Cepheids (∼5% per galaxy) without the limitations of the serendipitousness intrinsic of SNe, or the long observing campaigns needed for Cepheids. Moreover, it is used in a wide range of distances: from very local, up to values relevant for...
In this talk, we present an effective model for the sterile neutrino dark matter candidate. Due to new physics at the UV scale, three sterile neutrinos couple with SM fermions and gauge bosons via the SM gauge symmetric four-fermion interactions. Upon the spontaneous symmetry breaking, sterile neutrinos become massive and possess effective couplings to SM particles. We will show that the...
Abstract:
The origin of hydrodynamical instability and turbulence in the Keplerian accretion disk is a long-standing puzzle. The flow therein is linearly stable. Here we explore the evolution of perturbation in this flow in the presence of an additional force. Such a force, which is expected to be stochastic in nature hence behaving as noise, could result from thermal fluctuations (however...
The polarization measurement of the high-energy photons from cosmic sources is today recognised as a key goal for understanding the emission mechanisms and the geometry of the active regions involved, and therefore to solve still open hot scientific issues. To achieve this challenging objective, a mandatory requirement for new instrumentation in this energy regime will be to provide high...
The composition of neutron stars is an open research problem. In particular, the lack of information on the behavior of the symmetry energy above saturation density has prevented a reliable first-principle calculation of neutron stars equation of state. However, recently, new observational data has become available, which allows for better constraining of the internal properties of the star,...
We investigate the rotation of the polarization of a light ray propagating in the gravitational field of a circularly polarized laser beam. The rotation consists of a reciprocal part due to gravitational optical activity, and a non-reciprocal part due to the gravitational Faraday effect. We discuss how to distinguish the two effects: letting light propagate back and forth between two mirrors,...
Globular clusters are known to host an unusually large population of millisecond pulsar when compared to the Galactic disk. This is thanks to the high rate of dynamical encounters occurring in the clusters that can create the conditions to efficiently recycle neutron stars in millisecond pulsars. The result is a rich population of pulsars with properties and companions difficult to replicate...
If two particles collide near a rotating black hole, their energy in the centre of mass frame E_c.m. can become unbounded under certain conditions. In doing so, the Killing energy E of debris at infinity is, in general, remain restricted. If E is also unbounded, this is called the super-Penrose process. We elucidate when such a process is possible and give full classification of corresponding...
This abstract is primarily based on my recent paper IJMPD 30, 05 (2021) 2150034, along with arXiv: 2101.06272.
Over the past decades, various researchers have indirectly predicted at least a dozen super-Chandrasekhar white dwarfs (white dwarfs which violate the Chandrasekhar mass-limit) from the luminosity observations of type Ia supernovae. Several research groups worldwide proposed...
The detection of neutrinos produced by pp-chain and CNO-cycle provide us fundamental informations on the thermal stratification and on the chemical composition of the solar core.
These can be used to verify the predictions ot the so-called Standard Solar Models (SSMs), which represent a benchmark for stellar evolution, and to constrain standard and non/standard energy generation and...
We are experimentally investigating possible departures from the standard quantum mechanics’ predictions at the Gran Sasso underground laboratory in Italy.
In particular, with radiation detectors we are searching signals predicted by the collapse models (spontaneous emission of radiation) which were proposed to solve the “measurement problem” in quantum physics and signals coming from a...
Several observations using electromagnetic signal have led to a paradigm shift in our understanding of the Universe, with the realization that two unknown quantities - namely dark matter and dark energy - constitute about 95% of the Universe, even though their existence could not be explained by the known laws of physics and fundamental particles discovered until now. Moreover, measurements of...
I will talk about a recent work, where we have investigated the interaction between electromagnetic, gravitational, and plasma related perturbations on homogeneous and hypersurface orthogonal LRS class II spacetimes. By using these spacetimes, which allow for the inclusion of a non-zero magnetic field, as backgrounds in a perturbative approach, we are able to see interactions between the...
The TianQin mission plans to deploy three drag-free controlled satellites in circular high Earth orbits at an altitude of $10^5$ km. The satellites form a nearly equilateral-triangle constellation, and exchange high-precision laser interferometric links to detect low-frequency gravitational waves in the mHz frequency band. TianQin features a geocentric concept, and is facing the challenge of...
Energy shifts of radiation from accreting black holes may be caused by the fast orbital motion and the gravitational redshift near the event horizon. Individual clumps of matter experience the effects of general relativity as they gradually sink into a deep potential well. An episodic supply of material is maintained by tidal disruption events (TDE) and the emerging radiation is modulated in...
Einstein-aether theory is a vector-tensor theory with the vector (aether) field that is always timelike and unity. It is self-consistent (such as free of ghosts and instability), and satisfies all the experimental tests carried out so far. Its Cauchy problem is well posed, and energy is always positive (as far as the hypersurface-orthogonal aether field is concerned). In addition, BHs exist ...
Observation of high energy and very high emission from Gamma Ray Bursts (GRBs) is crucial to study the gigantic explosion and the underline processes. With a large field-of-view and almost full duty cycle, the Water Cherenkov Detector Array (WCDA), a sub-array of the Large High Altitude Air Shower Observatory (LHAASO), is appropriate to monitor the very high energy emission from unpredictable...
The gravitational three-body problem has a long history, extending all the way back to Sir Isaac Newton. In spite of hundreds of years of research, we still do not have a complete solution to the general case, where no restrictions are placed on the nature of the interaction. Historically, this has been attributed to the appearance of chaos in large regions of parameter space, implying that...
Analytical models of accretion disks have been an important tool to understand the basic underlying principles of accretion. Classically, these models are constructed using an isolated Kerr black hole. However, astrophysical black holes are usually surrounded by electromagnetic fields. We consider here the presence of electromagnetic test fields that are weak in the sense that they do not...
In this talk, I will present a novel approach to obtain constraints on the expansion rate of the Universe based on the differential age evolution of "cosmic chronometers". The strength of this method is that it allows a direct measurement of the Hubble parameter $H(z)$ without relying on any cosmological assumptions, providing an ideal framework to test cosmological models.
I will review the...
We define bulk-to-boundary maps corresponding to quantum gravity states in the tensorial group field theory formalism, for quantum geometric models sharing the same type of quantum states of loop quantum gravity. The maps are defined in terms of a partition of the quantum geometric data associated to an open graph into bulk and boundary ones, in the spin representation. After showing that such...
Hard X-/soft Gamma-ray astronomy is a key field for the study of important astrophysical phenomena such as the electromagnetic counterparts of gravitational waves, gamma-ray bursts, black holes physics and many more. However, the spatial localization, imaging capabilities and sensitivity of the measurements are strongly limited for the energy range >70 keV due to the lack of focusing...
PSR J0537-6910 is a young neutron star that regularly experiences pulsar glitches, and shows a rather high braking rate between them. Observed spin-down of the pulsar could be due to the r-mode oscillations, which in turn may generate gravitational waves in the sensitivity range of the LIGO and Virgo detectors.
Based on the analysis of the LIGO-Virgo-KAGRA observing run O3, and taking into...
Large-scale N-body simulations have successfully reconstructed cosmic structure formation with increasing resolution and complexity, as observations corroborate. Complementary efforts have arrived at a hydrodynamical theory that explains cosmic structure evolution up to the non-linear regime. While the statistical properties of mass density perturbations for the observable universe as a whole...
Even if, at the moment, globular cluster (GC) millisecond pulsars (MSPs) cannot be timed with an extremely high precision, mainly due to the effects induced on the MSPs dynamics by the GC gravitational potential, we expect that the situation will change in the near future thanks to new powerful detectors, like the Square Kilometre Array (SKA). Therefore, we suggest the possibility of including...
The evolution and equilibrium structure of dark matter halos has been well studied using N-body simulations. However, theoretical understanding, for example, based on statistical mechanics has been more challenging. A decade ago we showed that extremizing the number of microstates with a given energy per unit mass, under the constraints of conserved total energy and mass, leads to the maximum...
The theory of primordial inflation has been highly successful in resolving theoretical difficulties of standard FRW cosmology. Moreover, many of the general predictions of inflation have been confirmed by observation. However, higher precision measurements of the cosmic microwave background (CMB) now disfavor many inflation-driving potentials due to a suppression of the tensor-to-scalar...
The cosmological constant (CC) term, $\Lambda$, in Einstein's equations has been for some three decades a
fundamental building block of the concordance or standard $\Lambda$CDM model of cosmology. Even though the model is not free of fundamental problems, they have not been circumvented by any alternative dark energy
proposal either.
However, an interesting alternative is that the vacuum...
In this talk we will present the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, etc.
The CNO cycle consists of a series of nuclear reactions that provide energy in stars. There exist multiple different cycles depending on temperature and relative abundance of elements in stars. In the Sun the CNO cycle is a catalyst cycle where nuclear reactions cycle through carbon, nitrogen and oxygen. Initially, a free proton fuses with a carbon-12 nucleus starting a sequence of reactions...
It has been established that Gamma-Ray Bursts (GRB) can produce Very High Energy radiation (E > 100 GeV), opening a new window through which to investigate particle acceleration and radiation properties in the most energetic domain. We expect that next-generation instruments, such as the Cherenkov Telescope Array (CTA), will mark a huge improvement in their observation. However, constraints...
Massive and passive galaxies can be used as cosmic chronometers to study the expansion history of the Universe. In particular, by following their differential age evolution over different cosmic epochs it is possible to obtain direct measurements of the Hubble parameter, $H(z)$. However, robust age estimates require deep spectroscopy to break internal degeneracies between stellar population...
Numerous studies on hydrodynamics of the Keplerian as well as the sub-Keplerian accretion disc around a compact object (e.g., white dwarf (WD), neutron star (NS), or a black hole (BH)) attempted to explain the observed UV, soft and hard X-ray spectra. Although, when the compact object (e.g., a WD or an NS) has a finite surface, its rapid rotation, the stellar magnetic field could cause...
It is now clear beyond any doubt that neutrinos have masses, and that they mix. Experiments with solar, atmospheric, reactor and accelerator neutrinos have determined, with remarkable accuracy, values of $\Delta m_{ij}^2 = m_i^2 -m_j^2 $. Absolute neutrino masses, however, are still unknown. We know neutrino vacuum oscillations only depend on $\Delta m^2$, hence, oscillations experiments are...
It is expected that the quantum gravity should resolve the black-hole singularity problem, according to the finite action principle one may ask which of the microscopic actions remain finite for non-singular black holes and conversely interfere destructively for the singular ones. We also show that the finite action selection principle works for H-L gravity in the context of black holes (the...
Preliminary results of the investigation of the properties of 13 clusters of galaxies from CfA2 redshift survey are discussed in the presented article. The distributions on absolute magnitude and luminosity represent two areas for clusters ##88, 1101, 1046, 142, 933, 1242, 1652, 107, 150, 316, 317, 961, 977. Redshifts of these clusters are in the region 0.002 – 0.022. The distributions on...
The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) mission concept aims at fully exploiting Gamma-Ray Bursts (GRB) for early Universe and multi-messenger astrophysics, as well as providing a substantial advance in time-domain astronomy through detection, accurate location, multi-wavelength (0.3 keV – 10 MeV plus near IR) characterization, and redshift measurement, of many...
We reveal three new theorems on black hole rotation previously unexplored in the Hawking era. These results are based on the quasi-local energy investigation of the black hole in Kerr spacetime.
- The Horizon Mass Theorem states that the mass at the event horizon of any
black hole is always twice its irreducible mass. In particular, the irreducible
mass does not contain...
Gravitational wave astronomy is expected to provide independent constraints on neutron star properties, such as their equation of state. This is possible with the measurements of binary components' tidal deformability, which alter the point-particle gravitational waveforms of neutron-star binaries. I'll discuss some tidal deformability effects due to the elasticity/solidity of the hadronic...
$\Lambda CDM$ is increasingly challenged by observations in the late-time Universe. Here we consider unparticle cosmology for its potential to alleviate some of these issues. Unparticles offer a scale invariant contribution by an extra parameter $\delta$, here studied for $\delta \in [-6,1]$ (corresponding to scaling dimension $d_u \in [-2,3/2]$). For most values of $\delta$, the model...
The first detection of gravitational waves on 2015 with the Advanced LIGO and Advanced Virgo interferometers has opened a new observational window in the Universe. The last decade has also welcomed decisive discoveries in neutrino astronomy. Expected advances of gravitational wave and neutrino detectors by the end of the 2020s will mark the start of a golden era of multi-messenger...
The physical mechanism underlying pulsar glitches, abrupt spin-up events that interrupt the secular spin-down of some pulsars, is unknown. Plausible models include superfluid vortex avalanches, starquakes, or hydrodynamic instabilities. Almost all such models are reducible to a system in which stress accumulates between glitches and is partially (or fully) released at a glitch. The...
I discuss the simplest solution of the covariant Schroedinger equation of
quantum gravitational field derived using precanonical quantization,
a quantization based on the De Donder-Weyl Hamiltonian theory which
requires no space-time decomposition. This is a second-order PDE for
a Clifford algebra valued wave function on the space of space-time and spin-connection variables which...
We consider the possibility that dark matter is made of self-gravitating Bose-Einstein condensates (BECs) described by the Schrodinger-Poisson or Gross-Pitaevskii-Poisson equations. We determine the mass-radius relation of self-gravitating BECs with repulsive or attractive self-interaction at zero temperature. When the self-interaction is attractive, we evidence the existence of a maximum mass...
Over the last decade, experimental physics and observational cosmology have made many fundamental discoveries: gravitational waves (LIGO), Higgs bosons (LHC), photon condensates with rest energy and rest mass trapped in "mirror cavities" (Bonn University).
Through these remarkable results, Nature suggests that at pressures and temperatures well above the Higgs field level (246 GeV), only the...
The largest amount of antineutrinos detected about the Earth is emitted by the natural radioactive decays inside the Earth: more than 99% of the present-day Earth’s radiogenic heat is originated by the β$^{-}$ decays of $^{40}$K and of $^{232}$Th and $^{238}$U chains isotopes. Other flux components are provided by cosmic rays interactions in the atmosphere or by possible extra-terrestrial...
We calculate the elastic properties of the outer crust of Neutron Stars (NSs) under the approximation of the one component plasma (OCP) in the high density limit. An electron sector under a degenerate Fermi sea is considered. This is of interest for the modelling of the gravitational wave signal strength emitted in the violent events of NS mergers and NS continuous emission. We use Molecular...
The path integral approach yields a powerful framework in the quantum theory. It emphasizes Lorentz covariance and allows for the description of non-perturbative phenomena. In the path integral, one sums over all possible configurations of a field(s) Φ weighted by $e^{iS[Φ]}$, where S[Φ] is the classical action of the theory.
In the Minkowski path integral, the classical action approaching...
Aim to the MeV window of gamma-ray astronomy and the next generation of gamma-ray telescope, a prototype gamma-ray imaging detector—MeVCube funded by NSFC and DFG will be developed to demonstrates that even a tiny detector can reach the sensitivity of last generations large -scale instruments. I will present the preliminary design of MeVCube and the prospective performance yielded by...
By using a general relativistic approach to study Schwarzschild black hole (BH) rotation curves, we reveal the detection of the gravitational and the kinematic boosted redshifts in the strong gravitational regime of the Active Galactic Nucleus of NGC 4258, and estimate its BH mass-to-distance ratio in terms of astrophysical observable quantities.
The total relativistic redshift/blueshift...
The Planck mission found excellent agreement with a spatially flat Universe and fluctuations consistent with simple models of inflationary cosmology. The Planck data are well described by a six parameter model that has become known at the LCDM cosmology. Nevertheless, there have been claims of deviations (or tensions) with the LCDM cosmology both internally to the Planck data and with other...
The Hubble constant remains one of the most important parameters in the cosmological model, setting the size and age scales of the Universe. Present uncertainties in the cosmological model including the nature of dark energy, the properties of neutrinos and the scale of departures from flat geometry can be constrained by measurements of the Hubble constant made to higher precision than was...
In recent years, a determination of the Hubble constant from supernovae has become increasingly discrepant with that inferred from the cosmic microwave background. This “Hubble tension” is not easily attributable to any known systematic artifacts in either measurement and may thus be indicating some new physics beyond that in the standard cosmological model. Easy fixes based on late-time...
An important and unresolved question in cosmology today is whether there is new physics that is missing from our current standard Lambda Cold Dark Matter (LCDM) model. A current discrepancy in the measurement of the Hubble constant, Ho, could be signaling a new physical property of the universe or, more mundanely, unrecognized measurement uncertainties. I will discuss two of our most precise...
The key elusive cosmic constituents - dark matter, dark energy and black holes - play a fundamental role in shaping the visible universe. In this talk, I will discuss the current status of our understanding of the distribution of dark matter on small-scales in LCDM and the key open questions. Gravitational lensing by clusters of galaxies offers a powerful way to map dark matter and the high...
The standard cosmological model (the LCDM model) has been established and its parameters are now measured with unprecedented precision. However, there is a big difference between modelling and understanding and precision is not enough: accuracy is also crucial. The "unreasonable effectiveness” of the LCDM model offers challenges and opportunities. In particular, as statistical errors in...
IceCube detects more than 100,000 neutrinos per year in the GeV to 10 PeV energy range. Among those, we have isolated a flux of high-energy neutrinos of cosmic origin, with an energy densityin the extreme universe similar to that of high-energy photons and cosmic rays.We identified their first source:on September 22, 2017, following an IceCubeneutrino alert, observations by other astronomical...
There are three regions in the Kerr spinning black hole metric, separated by the two event horizons. The outer two are probably good approximations to the corresponding regions as a real black hole forms, but the inner Kerr is not. It has to have something to generate the gravitational field outside, and that can only be a singularity since it is by definition matter free. However, even after...
We reveal three new discoveries in black hole physics previously unexplored in the Hawking era. These results are based on the remarkable 1971 discovery of the irreducible mass of the black hole by Christodoulou and Ruffini,
1. The Horizon Mass Theorem states that the mass at the event horizon of any black hole: neutral, charged, or rotating, is always twice its irreducible mass observed at...
Since their discovery in the late '60s, Gamma-Ray Bursts constitute one of the most fascinating and mysterious phenomena for modern science, with strong implications for several fields of astrophysics and fundamental physics. In this review, I will focus on the perspective key-role of GRBs for cosmology and multi-messenger astrophysics. Indeed, the huge luminosity, the redshift distribution...
GRB190114C (z = 0.42) is the first GRB firmly detected at TeV energies. Like most long GRBs at low-to-intermediate redshifts, it exhibits a clearly detected accompanying supernova, SN2019jrj, whose properties are similar to those of known core-collapse supernovae. However, SN2019jrj differs from classical GRB-SNe (like the prototypical SN1998bw) in being less luminous and having narrower...
Relaxation mechanisms of collisionless self-gravitating systems of fermions in cosmology, can lead to spherical equilibrium states which are stable, long-lived, and able to explain the dark matter (DM) halos in galaxies. The most general fermionic DM profile out of such a mechanism, develops a degenerate compact core which is surrounded by an extended halo. When applied to the Milky Way, it is...
Inspired by the visionary efforts of building Arecibo, the Five-hundred-meter Aperture Spherical radio Telescope (FAST) was formally established in 2007; its construction commenced in 2011; achieved first light in 2016; started normal operation in 2020. The first internationally open call-for-proposal was released in March 2021. I report here a few science highlights so far, particularly from...
The dark matter and neutrinos are keys to the formation and evolution of the universe. Yet we do not know what is dark matter, and we do not fully understand the fundamental properties of neutrinos. PandaX is an underground xenon-based observatory located in the world deepest China Jinping Underground Laboratory in Sichuan, China. The current phase of PandaX consists of a 4-tonne scale...
Earth-based experiments have been continuously increasing their sensitivity to gravity phenomena at laboratory scales. A yet unexplored frontier is the regime of microscopic source masses, which enables studies of fundamental interactions and provides a path towards exploring the quantum nature of gravity. We have recently demonstrated gravitational coupling between a test mass and a 90mg gold...
General Relativity (GR) is a consequence of the Einstein Equivalence Principle. Accordingly, tests of GR are either test of its foundation or test of consequences of GR. In general, tests of the foundations are zero tests. Test of predictions of GR rely on certain notions like standard clocks or non-rotating frames which can be defined within GR and which are basic in the prediction of certain...
In the last decade, laser interferometry in space has advanced from planning on ground to an established technique for gravitational physics, both for the detection of gravitational waves (LISA project) as well as for global observation of the Earth gravity field (GRACE Follow-On). I will summarize the past and planned missions including LISA Pathfinder, GRACE Follow-On, Pathfinder missions in...
Dragging of inertial frames, or frame-dragging, is an intriguing and fascinating phenomenon of Einstein's theory of General Relativity (GR) with relevant astrophysical implications. Some theories of gravitation, alternative to GR but in agreement with its post-Newtonian tests, predict a different result from GR for frame-dragging. However, frame-dragging tests, in agreement with GR, have been...
With FAST, we detected 1652 pulses from FRB 121102 within a time span of 57 days and a total of about 50 observing hours. On two separate days, the peak burst rate reaching beyond 115 bursts per hour. The burst energy spans three orders of magnitude between ~5e36 to 6e 39 ergs. Tests with a hybrid of real and simulated bursts show that this burst set is 90% complete for E> 3 e37 ergs. The...
Along the last decades, several regular black hole (BH) solutions, i.e., singularity-free BHs, have been proposed and associated to nonlinear electrodynamics models minimally coupled to general relativity. Within this context, it is of interest to study how those nonlinear-electrodynamic-based regular BHs (RBHs) would interact with their astrophysical environment. We investigate the...
The PLANCK satellite has observed certain anomalies in the Cosmic Microwave Background (CMB) that bring out a tension between the standard six-parameter $\Lambda$CDM cosmological model and observations. The possibility that these anomalies could be tell-tale signatures of fundamental physics at the Planck scale is exciting. We show that this possibility is realized within Loop Quantum...
Current PyCBC-based searches detect gravitational-wave (GW) transients by matched-filtering the advanced LIGO-Virgo detector data with model waveforms. They have, to date, detected or confirmed more than 50 compact binary merger signals. But these searches perform poorly when it comes to identifying short-duration compact binary signals in Advanced LIGO-Virgo data. In this talk, we will...
Following the direct detection of gravitational waves, modification to General Relativity (GR) at strong gravity regimes is one of the most important aspects of gravity research. Chern Simons (CS) gravity is one of the most frequently studied parity-violating models of strong gravity. CS gravity is indistinguishable from GR for all conformally flat space-times and for space-times that possess...
With the advent of the Event Horizon Telescope, the study of multiply lensed images of emitting material about black holes has become a reality. The direct detection of a bright, ring-like structure in horizon-resolving images of M87* is a striking validation of general relativity. However, this success raises a singular difficulty: the angular size and shape of these rings are potentially...
Borexino, a large volume detector for low energy neutrino spectroscopy, is currently taking data underground since 2007 at the Laboratori Nazionali del Gran Sasso, Italy. The main goal of the experiment is the real-time measurement of solar neutrinos, especially the low energy part of the spectrum. Neutrinos are detected via neutrino-electron scattering in an ultra-pure organic liquid...
Ancient observations were transmitted to posterity through mythology, cities and temples’ orientations and mere time and position data. While stellar variability does not fit Aristotles’ aetherian-eternal nature of the last celestial sphere, Greek myths on the painful shoulder of Orion explained the observed Betelgeuse’s variability.
The meridian line in saint Peter’s square was designed by...
The opportunity of this session is to focus on
1) observations and their criticities in the AAVSO 130 years database on Betelgeuse
a) V-Band
b) R obs in daylight
c) Before AAVSO
d) visual near the horizon
2) time series analyses of Betelgeuse’s light curve
a) mathematical properties
b) other Supergiants: VY Canis Majoris, Eta Carinae
3) spectral data on Betelgeuse during the...
The Newtonian gravity potential is one of the main notions for conventional geodesy and employed for basic concepts, such as the definition of heights. A modern height definition in terms of geopotential numbers can offer a variety of advantages. Moreover, from the theoretical point of view, such a definition is considered more fundamental.
We know, however, that relativistic gravity (here...
We studied the formation of GW190521-like binary black holes (BHs) from Population (Pop) III binary stars by binary population synthesis technique. We adopted two kinds of Pop III star evolution models with different convective overshoot parameters, both of which can reproduce solar-metallicity star evolution if we change only metallicity from zero metallicity to the solar metallcity. We found...
Jayme Tiomno belonged to the ‘founders generation’ of physicists in Brazil. He began working in relativity theory early in his career, at a time when it was not at all ‘fashion-able’, through the influence of his early mentor, Mario Schenberg in São Paulo. When he went to graduate school in Princeton, early in 1948, his advisor there, John Wheeler, gave him a project in General Relativity,...
The Galactic halo is criss-crossed by long stellar streams that are probably the remnants of defunct globular clusters and dwarf galaxies. I will present the recent discoveries of these structures from Gaia mission data. While streams clearly inform us in a direct way about past accretions onto our Galaxy, their most promising property is that they allow us to measure the Galactic acceleration...
Neutron star observations offer us an excellent testbed to measure nuclear parameters that are difficult to access with terrestrial experiments. Some of these nuclear parameters have strong correlations with radii and tidal deformabilities of neutron stars. In this talk, I focus on one of such parameters, K_{sym,0}, that corresponds to the curvature of symmetry energy at nuclear saturation...
I will discuss the science case for a sensitive spectro-polarimetric survey of the microwave sky. Such a survey would provide a tomographic and dynamic census of the three-dimensional distribution of hot gas, velocity flows, early metals, dust, and mass distribution in the entire Hubble volume. It would also exploit CMB temperature and polarisation anisotropies down to fundamental limits, and...
Élie Cartan’s invariant integral formalism is extended to gauge field theory, including general relativity. This constitutes an alternative procedure that is equivalent to the Rosenfeld, Bergmann, Dirac algorithm. In addition, a Hamilton-Jacobi formalism is developed for constructing explicit phase space functions in general relativity that are invariant under the full four-dimensional...
We point out that in models of macroscopic topological defects composed of one or more scalar fields that interact with standard-model fields via scalar-type couplings, the back-action of ambient matter on the scalar field(s) produces an environmental dependence of the fundamental constants of nature, as well as spatial variations of the fundamental constants in the vicinity of dense bodies...
The most important results of nonlinear perturbative theory for alternative models to LCDM, in which a scalar field changes gravitational dynamics at cosmic scales, will be summarized. We focus on two-point statistical observables, such as the power spectrum and correlation function, and discuss the changes from the LCDM model.
We discuss different types of solutions (globally regular, black holes, wormholes and cosmological solutions), in the framework of the new two-parameter Palatini scalar-tensor theory with the derivative coupling of a scalar to the Ricci tensor. The metric version of the theory for generic values of two coupling constants is ghostly, but in Palatini version it is ghost-free. The theory admits...
Gamma-ray bursts (GRBs) associated with gravitational wave events are, and will likely continue to be, viewed at a larger inclination than GRBs without gravitational wave detections. As demonstrated by the afterglow of GRB 170817A, this requires an extension of the common GRB afterglow models where it typically used to be sufficient to assume that the observer was looking straight into a jet...
Primordial Black Holes (PBHs) have entered the forefront of theoretical cosmology, due their potential role in phenomena ranging from gravitational waves, to dark matter, to galaxy formation. While producing PBHs from inflationary fluctuations naively would seem to require a large deceleration of the inflaton from its velocity at the horizon exit of CMB scales, in this talk we demonstrate that...
Standard cosmology is based on the assumption that the dark fluids behave as standard, hard matter.
On the other hand, soft matter is a well studied field in condensed matter physics. We investigate the possibility of ``soft cosmology'', namely the appearance (intrinsically or effectively) of soft-matter properties in the dark sectors. We propose a novel parametrization introducing the...
By observing the gravitational waves from the coalescence of a compact binary merger, it is possible to directly infer the luminosity distance to the source. This measurement does not use a distance ladder; the calibration is provided directly from the theory of general relativity. We discuss the present state of the field of GW cosmology, and its future promise.
Static and uniformly rotating, cold and hot white dwarfs are investigated both in Newtonian gravity and general theory of relativity, employing the well-known Chandrasekhar equation of state. The mass-radius, mass-central density, radius-central density etc relations of stable white dwarfs with $\mu=A/Z=2$ and $\mu=56/26$ (where $A$ is the average atomic weight and $Z$ is the atomic charge)...
Semiclassical Physics in gravitational scenario, in its first approximation (1st order) cares only for the expectation value of stress energy tensor and ignores the inherent quantum fluctuations thereof. In the approach of stochastic gravity, on the other hand, these matter fluctuations are supposed to work as the source of geometry fluctuations and have the potential to render the results...
Type Ia supernovae (SNe Ia) are excellent cosmological distance indicators. With them, one can precisely measure the expansion history of the Universe and constrain cosmological parameters such as the current expansion rate, H0, and the dark energy equation-of-state parameter, w. I will present new results from four current and upcoming surveys. The Swope Supernova Survey is a large,...
The teaching of relativity usually starts with kinematics: The invariance of the speed of light, clock synchronization, time dilatation and length contraction, the relativity of simultaneity, Lorentz transformation and Minkowski diagram. The change of the reference frame is a central topic. Only afterwards problems of relativistic dynamics are discussed. Such an approach closely follows the...
I will present an end-to-end exploration of the simplest modified gravitational theory in Jordan-Brans-Dicke (JBD) gravity, from an analytical and numerical description of the background expansion and linear perturbations, to the nonlinear regime captured with a hybrid suite of $N$-body simulations, to the parameter constraints from existing cosmological probes. In the analysis, the nonlinear...
In this talk I will briefly review the knowledge on angular momentum transport acquired from helio- and asteroseismology of low mass stars. I will discuss how rotation is determined from the seismic data, what results it has brought us for the Sun first, than other stars thanks to the space-based photometry missions. I will present the current shortcomings of the models, the various solutions...
Many tentative quantum gravity theories, from the Wheeler-deWitt equation to Loop Quantum Gravity, do not specify a time variable, and yet they are predictive. The discussion to clarify this strangeness has been long, but has been resolved and the issue should not be controversial anymore. I give a rapid and simple overview of the solution.
The main features of the "Tutti Frutti method" which has allowed
reaching the 6PN level of accuracy (modulo a few still unknown parameters)
in the relativistic treatment of the two-body system will be briefly introduced and discussed.
Special attention will be devoted to recent developments in the PN-PM structure of scattering angle of hyperboliclike encounters.
According to Dorrit Hoffleit Mira is the educational star. But it requires the use of a telescope at its minimum, and a binocular for its maximum phase, to spot in in city lights. Betelgeuse is a semiregular variable star of first magnitude, in the most famous constellation, achievable from both hemispheres. It is available to the naked eye for nine months a year. Its magnitude estimate,...
I observe variable stars since 1997. The "candidacy" of Mira Ceti as Betlehem Star because close to Jupiter-Saturn triple conjunction of 6-7 b.C. started at Pontifical University of Lateran and continued in Yale (2001-2004). Maxima correlation function ruled out Mira for having two consecutive bright maxima, but this property was confirmed in the "oldest" Myra-type: R Leonis, R Hydrae and Chi...
The AAVSO database of stellar magnitudes starts, for Betelgeuse, in 1890 and includes both visual and digital measures. In scientific publications the few digital photometries are limited to some observations, not sufficent to have an homogeneous and smooth lightcurve.
The classical time series analysis has been adapted to the case of variable stars, recognizing the yearly signal of the...
Since last 10 years or so, we have been developing the possible existence of highly magnetized white dwarfs. While the primary aim was to explain peculiar overluminous type Ia supernovae, later on, they have been found to have multiple implications including soft gamma-ray repeaters and anomalous X-ray pulsars, and gravitational radiation. Recently, we have successfully simulated their...
In a backyard observatory in Mainz, Germany, several stars have been observed at daylight using a 250mm Newton telescope and a CCD camera (ATIK 460exm). To measure the intensity of the sky background, the intensity of a background aperture was compared to the intensity of the star aperture and normalized to the known star magnitude. In this way sky background values of 1.8 - 4.7 mag/arcsec2...
A union of matter bounce and ekpyrotic scenarios is often studied in an attempt to combine the most promising features of these two models. Since nonperturbative quantum geometric effects in loop quantum cosmology (LQC) result in natural bouncing scenarios without any violation of energy conditions or fine tuning, an investigation of matter-ekpyrotic bounce scenario is interesting to explore...
After three decades, the neutron star formed by SN 1987A has likely given us a first sign of its presence: a blob of warm dust near the center of the explosion. I will summarize our understanding of the explosion, the structure of the supernova remnant, and the characteristics of "the blob”. I will describe in detail the possible explanations for the excess of energy coming out of the blob:...
ABSTRACT
It appears that studying the data from the catalogue of Gamma-Ray Bursts (GRBs) can be used to study the birefringence phenomenon in the magnetosphere of the magnetars. By analysing the data from the McGill Online Magnetar and HEASARC Fermi Burst Catalogues, in this work we studied the angular distances between the nearest GRBs and magnetars in projection, built their...
The recent discovery of a Galactic fast radio burst (FRB) occurring simultaneously with an X-ray burst (XRB) from the Galactic magnetar SGR J1935+2154 implies that at least some FRBs arise from magnetar activities. We propose that FRBs are triggered by crust fracturing of magnetars, with the burst event rate depending on the magnetic field strength in the crust. Crust fracturing produces...
The β Cephei pulsating stars are unique targets to probe our knowledge of the interior of massive stars. By analysing their pulsations with asteroseismology, we can explore the mixing processes, e.g., convection and overshooting, in the core of these massive stars. Asteroseismology has delivered another success by revealing their internal rotation. I illustrate these results with a review of...
Stellar theory predicts the existence of a black hole mass gap in the range ~50 to ~120 solar masses resulting from pair instability supernovae. The binary black holes of LIGO-Virgo's first two observing runs supported this prediction, showing evidence for a dearth of component black hole masses above 45 solar masses. Meanwhile, among the 30+ new observations from the third observing run,...
Bondi's celebrated mass loss formula measures the rate of change of energy carried away from an isolated system (in asymptotically flat space-time) by gravitational radiation. In this talk, we generalize this idea to the de Sitter setting. We derive a formula for the total canonical energy, and its flux, of weak gravitational waves on a de Sitter background. Based on arXiv:2003.09548 [gr-qc],...
We explore the ability of future cosmological surveys to put string theory under pressure through the Swampland program. It is well known that constructing consistent string theory solutions in a de Sitter background is tremendously difficult. This led to speculative constraints on the shape of the potential felt by the dark energy scalar field. This is known as the "de-Sitter conjecture" and...
It is shown that the Kerr solution exists in the generalized hybrid metric-Palatini gravity theory and that for certain choices of the function $f(R,\mathcal R)$ that characterizes the theory, the Kerr solution can be stable against perturbations on the scalar degree of freedom of the theory. We start by verifying which are the most general conditions on the function $f(R,\mathcal R)$ that...
Spinning neutron stars are sources of long-duration continuous waves that may be detected by interferometric detectors. We focus on long, but not infinite duration signals and derive the precise signal-to-noise ratio (SNR) when the duration is not a priori known. We illustrate the effect of gaps in the data on the SNR.
Satellite Tests of Relativistic Gravity (SaToR-G) is a new experiment in fundamental physics of the National Scientific Committee 2 (CSN2) of the Italian National Institute for Nuclear Physics (INFN).
The experiment aims at testing gravitation beyond the predictions of Einstein’s Theory of General Relativity in its weak-field and slow-motion limit, searching for effects foreseen by...
Modern surveys provide access to high-quality measurements on large areas of the sky, sampling the galaxy distribution in detail also in the emptiest regions, voids. Void cosmology is becoming an increasingly active sector of galaxy clustering analysis: by measuring void properties, such as density profiles or void number counts, it is possible to constrain cosmological parameters. Cosmic...
In this talk I will consider a very popular scenario where the dark energy is a dynamical fluid whose energy density can be transferred to the dark matter, and vice versa, via a coupling function proportional to the energy density of the dark energy. In particular, I will discuss this model’s ability to address the $H_0$ and $S_8$ tensions showing that considering data from Planck, BAO and...
Betelgeuse is the nearest red supergiant, one of the brightest stars in our sky, and statistically speaking it would be expected to be "typical". Yet it exhibits many features that seem "curious", to say the least. For instance it has a high proper motion. It rotates fast. It has little dust. It dimmed unexpectedly. Is any of these, and other, phenomena atypical, and taken together does it...
Most astrophysical constraints on the warm dark matter particle mass have been limited to observations covering the last 12 billion years of the Universe. However, over the past few years, data from the Hubble Space Telescope and the EDGES (21cm) collaboration have allowed such constraints to be extended well into the first billion years, a crucial epoch inaccessible by any other means. In...
In this talk, I will talk about the recent developments in numerical simulations of PBHs under spherical symmetry on a FRW background. Specifically, I will focus on the threshold for PBH formation and the effect of the accretion and sizes of the PBHs formed in terms of the specific shape of the initial curvature profile.
Mathematical derivations alone do not necessarily lead to physical understanding. A tool that can replace the mathematical treatment of a physical process and at the same time increase physical understanding are interactive computer programs, also known as system dynamics software, such as Stella, Berkeley Madonna, Wensim, Dynasys, Powersim or Coach. Such interactive software solves...
The temporal asymmetry between past and future permeates virtually every aspect of the world of our experience. It has no counterpart, as far as we know, in the laws of fundamental physics. One reaction to this is to trace this asymmetry to a fact about the early state of the universe, either taken as a brute, unexplained fact, or as a consequence of some physical principle. In this talk I...
About 99 percent of solar energy is produced through sequences of nuclear processes that convert hydrogen into helium in the so-called pp-chain. The neutrinos emitted in five of these reactions represent a unique probe of the Sun’s internal working and, at the same time, offer an intense natural neutrino beam for fundamental physics research.
The Borexino experiment consists of a large-volume...
The cosmic microwave background (CMB) acts as a backlight to the entire observable universe, and the ideas for using its distortion signatures, imprinted upon by the intervening large-scale structure, are an endless source of astrophysical probes that are limited only by our experimental reach. I review some of the ideas collected while responding to ESA's Voyage 2050 proposal call,...
The extraordinary advances in quantum control of matter and light have been transformative for precision measurements enabling probes of the most basic laws of Nature to gain fundamental understanding of the physical Universe. The development of atomic clocks with systematic uncertainties in the 10$^{-18}$ range enables searches for the variation of fundamental constants, dark matter, and...
In this talk we will explicitly show how ghost degrees of freedom arise in a sub-class of metric-affine theories unless projective symmetry is enforced. Then, we will generalise the techniques employed in that particular case to argue why ghosts will arise in generic metric-affine theories of gravity around arbitrary backgrounds. We will also discuss some results on possible ways to avoid them.
Theoretical and numerical works on the two-body problem in general relativity (GR) play a very important role when detecting and interpreting the gravitational wave signals. In this talk, we review the present state-of-the-art on traditional post-Newtonian (PN) methods in GR, applied to the gravitational wave and phase evolotion of inspiralling compact binaries. In particular, we emphasize...
It is commonly known that the Steady-state model was proposed and championed in a series of Influential papers around mid-twenty century by Fred Hoyle, Hermann Bondi and Thomas Gold. In contrast it is little known that, many years before, Albert Einstein briefly explored the same idea, that is of a dynamic steady state universe. Einstein tried to develop a model where the universe expanded and...
The current Gravitational Wave (GW) surveys of Binary Black Hole (BBH) mergers provide unprecedented probes of the dynamics in extreme gravitational fields and relativistic velocities. It will be presented a new method to search for possible low energetic signal with unknown morphologies features in the post merger phase of the gravitational wave signal from a BBH coalescences. Such transient...
Betelgeuse is a familiar M-type red supergiant and also the tenth brightest star in the sky. Nevertheless, it is also a very peculiar star. Its kinematics and the bow shock around it indicate that it is a runaway star moving at more than 30 km/s relative to the local standard of rest. At the same time, its rotation rates, also supported by the enhanced nitrogen abundances, are too high...
Simulated images of a black hole surrounded by optically thin emission typically display two main features: a central brightness depression and a narrow, bright "photon ring" consisting of strongly lensed images superposed on top of the direct emission. The photon ring closely tracks a theoretical curve on the image plane corresponding to light rays that asymptote to unstably bound photon...
In this talk we discuss three different models for a reduced phase space quantization of loop quantum cosmology (LQC) for a spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) universe filled with reference fields and an inflaton field in a Starobinsky inflationary potential. All three models are two-fluid models and they differ by their choice of global clock which are chosen to be...
The equilibrium configuration of white dwarfs composed of anisotropic fluid distribution in the presence of a strong magnetic field is investigated in this work. By considering a functional form of the anisotropic stress and magnetic field profile, some physical properties of magnetized white dwarfs, such as mass, radius, density, radial and tangential pressures, were derived; their...
In a non-empty universe, the Hubble expansion is dynamic. Under the current cosmological paradigm, the expansion decelerated when the universe was matter-dominated but is now accelerating due to dark energy. The dynamic expansion can be observed directly as a secular cosmological redshift drift, and this measurement does not rely on the cosmological distance ladder or any cosmological model....
We show that a magnetic charge in curved spacetime could be an artefact of a vacuum phase with zero metric determinant at a distance. This phase is characterized by a solution of the first order field equations with nontrivial torsion. The monopole charge has a topological origin, given precisely by a lower-dimensional counterpart of the Nieh-Yan invariant in absence of matter. In this...
Fast radio bursts (FRBs) are surprisingly abundant, highly energetic extragalactic signals, the nature of which still remains a mystery. The use of radio interferometers to identify the host galaxies of FRBs and characterise their local environments plays a key role in identifying the progenitor(s) of FRBs. The bursts themselves exhibit complex time-frequency structure and polarimetric...
We propose a method for localising a long-duration signal (longer than a few hours) when the start time and duration of the signal are unknown. We show how the uncertainties in the time-localization of the signal reflect on signal-to-noise ratio (SNR) of the recovered signal.
G4S_2.0 is a new project funded by the Italian Space Agency (ASI) that aims to perform a set of gravitational measurements with the Galileo satellites of the Full Operational Capability (FOC) constellation. Two of these satellites, GSAT 0201 and GSAT 0202, are characterized by a relatively high eccentricity of their orbits, about 0.16, with respect to that of the other satellites of the...
We will discuss the initial rotation rates of massive stars, and the change of the rotation rates in single and binary
stars during their evolution, in connection to Be stars, accretion-induced spin-up and stellar mergers. We will then
consider the evolution of the core rotation of massive stars, and the corresponding expectations for the spins of compact
objects. In the end, we with...
Nowadays one of the greatest mysteries of science is to find out why the universe has an accelerated expansion. In this talk we show that by considering the quantum nature of the gravitational field, we can associate an effective Compton mass to the wavelength of the graviton. The Compton Mass Dark Energy (CMaDE) model proposes that this mass can be interpreted as dark energy, with a
Compton...
The origin of the dimming and brightening event of 2019–20 in Betelgeuse has been subject to much speculation. Various causes, such as external dust or spots on the surface of the star, have been proposed for this sudden change in luminosity. We examine the light curve of Betelgeuse from 1990 for variations in the nonlinear dynamics of the star. Critical transitions in dynamical systems are...
In this presentation I analyze the robustness of the value of the Hubble-Lemaitre constant yielded by the cosmic distance ladder for Type Ia supernovae, which involves three rungs. In this analysis I hold fixed Rung 1 as the distance to the LMC determined to 1% using Detached Eclipsing Binary stars, in order to focus on the highest rungs. For Rung 2 I analyze two methods, the TRGB and Cepheid...
We present evidence that semiclassical gravity can give place to ultracompact stars, indistinguishable from black holes up to current observations. We integrate the semiclassical equations of (spherically symmetric) stellar equilibrium for a constant-density classical fluid. The semiclassical contribution is modelled by a quantum massless scalar field in a genuinely-static vacuum state...
An optical medium can be represented by a Riemannian manifold $(\mathcal{B}, g)$ where $\mathcal{B}$ is consider to be the physical space and $g$ the optical spatial metric. A geodesic flow in the unitary tangent bundle can be represented by a contact transformation in the space of contact elements. This fact, allows us to describe the wavefront evolution in an optical medium solely in terms...
I will discuss recent and ongoing work focused on attempts to restore concordance amongst cosmological data sets in the context of the H0 and S8 tensions. Particular attention will be paid to models invoking new physics at or prior to recombination, including small-scale baryon-clumping models (e.g., due to primordial magnetic fields) and quasi-accelerating early dark energy models.
The COSmic Monopole Observer (COSMO) is an experiment to measure spectral distortions of the Cosmic Microwave Background (CMB). Deviations from a pure blackbody spectrum are expected at low level (< 1 ppm) due to several astrophysical and cosmological phenomena, and promise to provide important independent information on the early and late phases of the universe. They have never been detected...
The enhancement of the spectrum of primordial comoving curvature perturbation $\mathcal{R}$ can induce the production of primordial black holes (PBH) which could account for part of present day dark matter.
As an example of the effects of the modification of gravity on the production of PBHs, we investigate the effects on the spectrum of $\mathcal{R}$ produced by the modification of gravity...
Einstein's theory of space-time curvature and its impressive astrophysical and philosophical consequences, not only since the experimental evidence of gravitational waves and the first image of a black hole, represent milestones in human knowledge, and the presentation of these insights in a popular scientific manner is an important undertaking. How can bizarre concepts such as the curvature...
The imaging formation process for some DM profiles is carried out.
We use the analytic information given for the surface mass density in each case (some classic profiles, and some recently proposed), to obtain the geometrical and physical characterization that could provide information to identify new types of DM. The goal of this work is to understand if there are trails of the physical...
The isolated formation channel is one of the most studied formation
scenarios for stellar mass black hole binary (BBH) mergers detected by LIGO and Virgo. Focusing on the effects of
uncertain stellar and binary physics, we investigate this BBH formation channel using the rapid binary population
synthesis code SeBa.
Regardless of our assumptions, the two must common formation path...
There is an increasing interest in very early stages of the Universe in which the energy density of the inflaton could be dominated by its kinetic part. This includes classical inflationary scenarios with deviations from slow-roll regimes that can introduce modifications to the power spectra of the primordial fluctuations. Another example are quantum bouncing cosmologies. For instance, this is...
The shadow around the supermassive black hole in M87 was reconstructed in 2019 based on its observations with the Event Horizon Telescope in 2017. Recently polarization map for the M87* shadow was presented. We discuss opportunities to evaluate parameters of alternative theories of gravity with shadow observations, in particular, a tidal charge could be estimated from these observations.
Notion of Time in fundamental physics has undergone radical revisions over centuries and issues at the forefront of cosmology and quantum gravity pose new conceptual and technical challenges. This talk will provide an short overview of the evolution of ideas and the current status.
In this talk, we present the recent determination of the spin period of CTCV J2056-3014, a magnetic white dwarf in a cataclymisc binary system. Its X-ray and optical emission is clearly modulated with a 29.6 s period and points to an accretion origin. We briefly discuss this object in the context of other fast-spinning white dwarfs.
Solar neutrinos provide a sample of electron neutrinos of different energies. They are therefore a unique probe of the electron neutrino propagation through solar matter and for the experimental study of the MSW effect. Borexino, with its unique purity and sensitivity, has been able to study individually all components, extracting the best test of electron neutrino survival probability to...
We developed a CMB Boltzmann solver to test gravity theories in the framework of the degenerate higher-order scalar-tensor (DHOST) theory. This theoretical framework includes the wide class of dark energy models such as the Horndeski theory and its extensions as certain limits, and the general relativity can be also recovered. In this talk, we show how to formulate the linear perturbations of...
NASA-DLR's Stratospheric Observatory for Infrared Astronomy (SOFIA) observed Betelgeuse during the 2019/2020 Great V-Band Dimming event. High spectral resolution emission-line spectra were obtained with EXES at [Fe II] 25.99 microns and [S I] 25.25 microns before and during the event, and with upGREAT at [O I] 63.2 microns and [C II] 157.5 microns shortly after minimum. The line fluxes and...
Peter Bergmann initiated in 1966 an application of Hamilton-Jacobi techniques to general relativity. Little had been done by this time on extending this analysis to gauge theories. He proved that when, as in the case of Einstein’s theory, the phase space generator of evolution consisted of a linear combination of constraints, the Hamilton principal function must be independent of spacetime...
As an alternative to the popular parametrisations of the dark energy equation of state, we construct a quintessence model where the scalar field has a linear dependence on the number of e-folds. Constraints on more complex models are typically limited by the degeneracies that increase with the number of parameters. The proposed parametrisation conveniently constrains the dark energy...
With recent observations of gravitational wave signals from binary neutron star(BNS) mergers and observations by NICER, the nuclear equation of state(EoS) is becoming increasingly testable by numerical simulations. Numerous simulations currently exist exploring the equations of state at different density regimes for the constituent neutron stars. In this work we perform full GR...
We present several families of black hole solutions in metric-affine theories of gravity with independent metric and affine connection. We show that the resolution of the singularity problem is a common feature of many such solutions, and discuss several strategies in terms of their observational discriminators as compared to GR canonical objects.
We focus on the energy flows in the Universe as a simple quantum system and are concentrating on the nonlinear Hamilton–Jacobi equation, which appears in the standard quantum formalism based on the Schrodinger equation. The cases of the domination of radiation, barotropic fluid, and the quantum matter-energy are considered too. As a result, the generalized Heisenberg uncertainty principle...
The origin of Fast Radio Bursts (FRBs) remains a mystery even as we are collecting important roadsigns that point towards preferred source models. A key piece of the puzzle is the search for their multi-wavelength counterparts. Many observations at high energies of FRB sources have been performed to date, but two recent discoveries perhaps provide the most information: the detection last year...
Searches for violations of Einstein’s equivalence principle, such as tests of local Lorentz invariance and local position invariance, have become one of the leading applications of low-energy, high-precision experiments with laser-cooled atoms. In our laboratory, we operate atomic clocks based on the microwave ground state hyperfine splitting frequency of Caesium and optical clocks based on...
Intermediate-mass black holes (IMBHs) span the approximate mass range $100$--$10^5$ $M_{\odot}$, between black holes (BHs) formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of massive BHs in a binary system are the most energetic gravitational-wave sources accessible by the ground-based gravitational-wave detector network, so is IMBH binary. The third...
Ring laser Gyroscopes (RLG) are very versatile devices that find application in many fields as navigation, seismology and geophysics. Moreover, thanks to their sensitivity and accuracy, in the last years they have been used in fundamental physics research field.
GINGER (Gyroscopes IN GEneral Relativity) research group aims to exploit a large RLG to test general relativity theory. Our research...
The status of the EFT approach to the compact binary problem will be assessed, with a discussion of recent progress in the study of both conservative and radiative dynamics, and a glimpse on possible future developments.
The arrival time delays of multiply imaged strong gravitationally lensed sources provides a one-step cosmological distance measurement. The methodology, known as time-delay cosmography, rose to prominence to provide precise measurements of the Hubble constant, independent of the local distance ladder and the cosmic microwave background. I introduce the methodology and key ingredients, as well...
We prove the following result. For a stationary, axisymmetric, asymptotically flat, ultracompact object (i.e. an object with light-rings) with a $\mathbb{Z}_2$ symmetry fixing an equatorial plane, the possibility and stability of timelike circular orbits in the vicinity of the existing light-rings, for both rotation directions, depend exclusively on the stability of the light-ring itself. An...
Our talk will start with a (hopefully) pedagogical introduction to the
topic of asymptotically de Sitter spacetimes. Afterward, we will
construct 'conserved' charges a'la Wald and Zoupas at a conformal
infinity and prove their uniqueness under a natural set of
assumptions. We will finish with a small comment on how to distinguish
the de Sitter group within a group of all asymptotic...
We report how to alleviate both the H0 and sigma8 tensions simultaneously within
torsional gravity from the perspective of effective field theory. Following these observations, we construct concrete models of Lagrangians of torsional gravity. Specifically, we consider a novel f(T) parametrization where two out of the three parameters are independent. This modified gravity model can...
Spectral distortions (SDs) of the cosmic microwave background (CMB) provide a powerful tool for studying particle physics. We study the distortion signals from decaying particles that convert directly into photons at different epochs during cosmic history, focusing on injection energies Einj ≲ 20 keV. We consider the effect of blackbody-induced stimulated decay, which can modify the injection...
The initial conditions are a subtle issue in loop quantum cosmology (LQC) and modified loop quantum cosmologies (mLQCs). This is mainly because in general there doesn't exist a preferred initial time and state for a quantum field in an arbitrarily curved space-time. If the universe is sufficiently smooth and its evolution is sufficiently slow, so the characteristic scale of perturbations...
The LIGO-Virgo Collaboration has so far detected around 90 black holes, some of which have masses larger than what were expected from the collapse of stars. The mass distribution of LIGO-Virgo black holes appears to have a peak at ∼ $30M_\odot$ and two tails on the ends. By assuming that they all have a primordial origin, we analyze the GWTC-1 (O1&O2) and GWTC-2 (O3a) datasets by performing...
In this presentation the white dwarf close binaries AE Aquarii and AR Sco are investigated to search for signatures of particle acceleration and associated non-thermal emission. A detailed investigation of the total Fermi-LAT data base reveal signatures of pulsed gamma-ray emission in AE Aquarii, which mimics earlier reports of transient burst-like pulsed TeV gamma-ray emission reported from...
We find that the famous giant star Betelgeuse is closer, smaller, and less massive than previously thought. Our theoretical predictions include results from three different modeling techniques: evolutionary, oscillatory, and hydrodynamic simulations conducted with the Modules for Experiments in Stellar Astrophysics (MESA) software suite. We use MESA stellar models and statistical techniques to...
In general relativity, the paths of light and freely falling particles are described as geodesics in curved spacetime. Sector models allow the construction of these geodesics without having to introduce the usual mathematical apparatus. Virtual sector models, provided by the web-based application ViSeMo, enable students to explore physical phenomena in a given spacetime. Examples include light...
In this contribution we report about Feynman’s route to gravitation [1], which can be traced back to the Chapel Hill Conference of 1957 [2]. As well known, Feynman was concerned about the relation of gravitation with the rest of physics. Probably for this reason, he promoted an unusual, field theoretical approach to general relativity, in which, after the recognition that the graviton must be...
We use Weinberg’s trick for adiabatic modes in a Manton approximation for general relativity on manifolds with spatial boundary. This results in a description of the time dependent solutions as null geodesics on the space of boundary diffeomorphisms, with respect to a metric we prove to be composed solely of the boundary data. We show how the solutions in the bulk space is determined with...
By applying the covariant Taylor expansion method of the heat kernel, Einstein anomaly associated with the Weyl fermion of spin 1/2 interacting with tensor fields of 1 , 3 and 5 order in six dimensional curved space are given. From the relation between Einsterin and Lorentz anomalies, which are the gravitational anomalies, all terms of the Einsterin anomaly should form total derivatives.
The Borexino has recently reported the first experimental evidence of neutrinos from the CNO cycle. Since this process accounts only for about 1% of the total energy production in the Sun, the associated neutrino flux, is extremely low as compared with the one from the pp-chain, the dominant process of hydrogen burning.
This experimental evidence of the CNO neutrinos was obtained using the...
The LIGO/Virgo collaboration is making astonishing discoveries at a fantastic pace, including a heavy binary black hole merger with component masses in the “black hole mass gap,” which cannot be explained by standard stellar structure theory. In this talk, I will discuss how new light particles that couple to the Standard Model can act as an additional source of energy loss in the cores of...
Higgs inflation is known to be a minimal extension of the Standard Model allowing for the description of the early Universe inflation. This model is considered as an effective field theory since it has a relatively low cutoff scale, thus requiring further extensions to be a valid description of the reheating phase. We present a novel unified approach to the problem of unitarization and UV...
We present a phenomenological but thorough analysis of current observational constraints on classes of FLRW cosmological models in which the matter side of Einstein's equations includes, in addition to the canonical term, a term proportional to some function of the energy-momentum tensor ($T^2\equiv T_{\alpha\beta}T^{\alpha\beta}=\rho^2+3p^2$), or of its trace ($T=\rho-3p$). Qualitatively, we...
The Coherent WaveBurst (cWB) search algorithm identifies generic gravitational wave (GW) signals in the LIGO-Virgo data by looking for excess power events in the time-frequency domain, with minimal assumptions on the signal model. The standard cWB pipeline improves signal significance by removing excess noise through the application of a set of a priori defined vetoes on summary statistics...
A hybrid star consisting of a defined quark matter core and a hadronic matter envelope has a unique internal structure that can have some influence on its observable properties. One possibility is the tidal effect during binary compact star coalescence, which is encoded in the phase of the emitted gravitational wave signal. In particular, the dynamical part of the tide which comes from the...
Fast Radio Bursts (FRBs) are extremely energetic, millisecond-duration events of unknown origin. Some FRB sources emit repeat bursts, which offer great opportunities for follow-up observations. The Canadian Hydrogen Intensity Mapping Experiment (CHIME), with 1024 beams observing the sky simultaneously has increased the number of known repeating FRBs by orders of magnitude. The regular daily...
Supermassive stars (SMSs), with masses $>10^5$ M$_\odot$, have been proposed as the possible progenitors of the most extreme supermassive black holes observed at redshifts $z>6-7$. In this scenario ('direct collapse'), a SMS accrete at rates $>0.1$ M$_\odot$ yr$^{-1}$ until it collapses to a black hole via the general-relativistic (GR) instability. Rotation plays a crucial role in the...
In this talk, we discuss cosmological constraints inferred from detection of galaxy clusters in the mm-wavelengths (through the thermal Sunyaev-Zeldovich effect), using Planck observations.
We focus in particular on the well known sigma8 tension. We provide a novel analysis of Planck clusters (also in combination with the power spectrum of the total tSZ signal), showing that constraints are...
Current measurements of the CMB anisotropies have given us unprecedented precision surrounding the standard ΛCDM model of cosmology and the parameters that make up this model. The data accrued by collaborations like Planck have even allowed us to test additional models of fundamental physics. These models have grown more recently in the context of diluting the tension between low-redshift and...
The Universe is homogeneous and isotropic on large scales, so on those scales it is usually modelled as a Friedmann-Lemaître-Robertson-Walker (FLRW) space-time. The non-linearity of the Einstein field equations raises concern over averaging over small-scale deviations form homogeneity and isotropy, with possible implications on the applicability of the FLRW metric to the Universe, even on...
We present a new measurement of the Hubble constant $(H_0)$ using supernovae type Ia (SNe Ia) based on the Surface Brightness Fluctuations (SBF) distance measurement method. We build a sample of calibrating anchors consisting of 24 SNe hosted in galaxies having SBF distance measurements. Applying a hierarchical Bayesian approach, we calibrate the SNe peak luminosity and extend it into the...
The nonextremal Kerr black holes have been considered to be holographically dual to two-dimensional (2D) conformal field theories (CFTs). In this talk, we extend the holography to the case of an asymptotically anti--de Sitter (AdS) rotating charged black holes in f(T)=T+αT^2 gravity, where α is a constant. We find that the scalar wave radial equation at the near-horizon region implies the...
The quest of the perturbative post-Minkowskian study of the gravitational two body problem
has recently seen advances upon employing perturbative quantum field theory techniques. I report on a
novel approach based on a worldline quantum field theory that provides an efficient way to
study the classical scattering of two massive objects (BHs, neutron stars or stars) in GR. We are able to...
Velocity field provides an alternative avenue to constrain cosmological information, and one of the commonly used statistics is the mean radial pairwise velocity. In this talk, we consider the three-point mean relative velocity (i.e. the mean relative velocities between pairs in a triplet), and show that it is a novel probe of neutrino mass estimation. We explore the full cosmological...
We report on the first direct search for low-mass scalar field dark matter utilising a gravitational-wave detector. We set new upper limits for the coupling constants of scalar field dark matter as a function of its mass by excluding the presence of signals that would be produced through the direct coupling of this dark matter to the beamsplitter of the GEO600 interferometer. The new...
The paradigm of slow-roll inflation provides a snapshot of the early universe that is in good agreement with present observations. Despite its success, most of the models studied so far rely heavily on the assumption that the universe is perfectly isotropic at early times. In this talk, I will discuss recent advances in anisotropic inflationary models. We adopt a Fock quantization for...
In the last two decades, Modified Gravity (MG) models have been proposed to explain the accelerated expansion of the Universe. However, one of the main difficulties these theories face is that they must reduce to General Relativity (GR) at sufficiently high energy densities, as those found in the solar system. To achieve this, MG usually employs the so-called screening mechanisms: non-linear...
Electron captures by atomic nuclei in dense matter are among the most important processes governing the late evolution of stars. Although these reactions have been known for a long time, most studies have focused on nonmagnetized matter. However, some white dwarfs are endowed with magnetic fields of the order of $10^9$~G. Even more extreme magnetic fields might exist in super Chandrasekhar...
In this talk I will discuss a systematic and rigorous classification of all the possible choices for averaging observables in cosmology. In this regard, the use of the so-called Geodesic Light-cone gauge provides simple expressions as I will show here. These new results will be compared with the recent literature. Moreover, I will discuss their impact on the bias that they can induce in the...
A recently introduced local measurement theory of quantum fields on possibly curved spacetime is the "FV framework" of Fewster and Verch [ [CMP 378, 851 (2020)]][1]. It is founded on the operational idea that every reasonable interaction with a quantum field of interest (system) is realised by temporarily coupling it to a probe field in a local manner. In this talk I will demonstrate the...
Detection of gravitational waves (GW) from compact binary mergers provide a new window into multi-messenger astrophysics. The standard technique to determine the merger parameters is matched filtering, consisting in comparing the signal to a template bank. This approach can be time consuming and computationally expensive due to the large amount of experimental data which needs to be analyzed....
The Event Horizon Telescope (EHT) has imaged the shadow of the supermassive black hole in M87 and aims to image the Galactic Center black hole Sagittarius A (Sgr A) as well. As a ground-based VLBI array, the resolution of the current EHT is limited by the size of the Earth and the maximum attainable observing frequency, which is set by the severity of tropospheric corruptions beyond...
The introduction of Special Relativity inevitably leads to phenomena that contradict everyday experience. Immersive virtual environments provide a laboratory where relativistic effects can be investigated directly and thus, a higher level of understanding for these unfamiliar concepts is achievable.
Using the method of ray tracing, computer graphics applications are able to generate...
We introduce a gravitational waveform inversion strategy that discovers mechanical models of binary black hole (BBH) systems. We show that only a single time series of (possibly noisy) waveform data is necessary to construct the equations of motion for a BBH system. Starting with a class of universal differential equations parameterized by feed-forward neural networks, our strategy involves...
Recurrent magnetar short bursts in the X-ray are one of the defining features of magnetars. I will give a brief background on this phenomenology, some recent results, and discuss how they likely connect to FRBs. I will also highlight the low-twist magnetospheric magnetar model for FRBs which associates FRBs with short bursts that transpire in particular low charge density states of mature...
Over the past few years, we have enjoyed a wide variety of gravitational-wave detections of compact binary coalescences. However, the wait continues for the first observation of a rotating neutron star via gravitational waves and, so far, only upper limits on the size of the involved deformations have been obtained. For these reasons, the maximum quadrupole deformation (or mountain) that a...
Core-collapse supernova form a diverse class of explosions produced at the end of the lives of massive stars. We study numerically the process of formation of the compact remnants (proto-magnetars and black holes) resulting from the collapse of very compact, low-metallicity cores of high-mass stars. We aim at understanding the dependence of the stellar remnants properties on the stellar...
Hypermassive hybrid stars (HMHS) are extreme astrophysical objects that could be produced in the merger of a binary system of two neutron stars. In contrast to their purely hadronic counterparts, hypermassive neutron stars (HMNS), these highly differentially rotating objects contain deconfined strange quark matter in their slowly rotating inner region. HMHS and HMNS are both metastable...
If an astrophysical environment is hot enough, screening in the associated nuclear reactions can be modified by the presence of a relativistic electron-positron plasma. Additionally, strong magnetic fields can create an additional enhancement as the electron and positron energy distribution is modified by the altered Landau level occupancy. This can result in a further enhancement of nuclear...
Time is one the oldest and most eminent concepts in both philosophy and physics. In my talk I will highlight some pertinent discussions from philosophy and how they relate to issues in current physics. More specifically, I will introduce two different types of temporal orderings and will explain why both are relevant for everyday life, whereas only one of them seems to be of importance to physics.
Baryon Acoustic Oscillations (BAO) involve measuring the spatial distribution of galaxies to determine the growth rate of cosmic structure. We derive constraints on cosmological parameters from 17 uncorrelated BAO measurements that were collected from 333 published data points in the effective redshift range 0.106≤z≤2.36. We test the correlation of the subset using random covariance matrix....
The debate on gravity theories to extend or modify general relativity is very active today and research efforts are devoted to test theories of gravity. Here, we present the GINGER experiment, which, being Earth based, requires little modeling of external perturbation, allowing a thorough analysis of the systematics, crucial for experiments where sensitivity breakthrough is required.
We...
We propose a late time gravitational transition at low redshifts $z_t<0.1$ as a possible solution of both the Hubble and growth tensions. Such a transition would naturally lead to a transition of the intrinsic SnIa luminosity and absolute magnitude $M$ at $z_t$ and could also be accompanied by a transition in the dark energy equation of state parameter $w$. Thus we would have a late $w - M$...
Although both early and late-time modifications of the ΛCDM model have been proposed to address the Hubble tension, compelling arguments suggest that for a solution to be successful it needs to modify the expansion history of the universe prior to recombination. This greatly increases the importance of precise CMB observations, and in this talk I will make the argument for CMB spectral...
The detection of neutrinos produced by pp-chain and CNO-cycle provide us fundamental informations on the thermal stratification and on the chemical composition of the solar core.
These can be used to verify the predictions ot the so-called Standard Solar Models (SSMs), which represent a benchmark for stellar evolution, and to constrain standard and non/standard energy generation and...
We comment on the recently introduced Gauss-Bonnet gravity in four dimensions. We argue that although the naive D->4 limit of the Gauss-Bonnet gravity does not work, a well-defined theory is obtained by generalizing a conformal trick employed by Mann and Ross to obtain a limit of the Einstein gravity in D=2 dimensions. This yields a scalar-tensor theory of the Horndeski type that can also be...
In the talk, I will discuss the primordial power spectra in two modified models of loop cosmology. As compared with the standard loop quantum cosmology in a spatially flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) universe, these two models arise from a separate treatment of the Lorentzian term in the Hamiltonian constraint. Both dressed metric approach and the hybrid approach are employed...
We give an account of Richard Feynman’s involvement with gravitational waves, which can be traced back to 1957, when he attended the famous Chapel Hill conference on the Role of Gravitation in Physics [1]. Feynman’s contribution was further developed in a subsequent letter to Victor Weisskopf [2], completed in February 1961, as well as in his Caltech Lectures on Gravitation [3], delivered in...
Betelgeuse (alpha Ori; M2-M4Iab) is the brightest red supergiant (RSG) and (probable) core-collapse supernova (SN) progenitor. In <105-yrs. Betelgeuse should explode and shine nearly as bright as the full moon. Last year Betelgeuse underwent an unprecedented dimming, decreasing in brightness by more than 50% (~1.0 mag) by Feb-2020. This notorious “Great Dimming” caught the attention of...
The spatial distribution of matter depicts a complex pattern commonly referred to as the 'cosmic web' in which massive nodes are linked together by elongated filaments found at the intersection of thin mildly-dense walls, themselves surrounding large and empty voids.
The intrinsically different gravitational dynamics history that each environment experience leaves an imprint on the present...
The scalar field dark matter also called ultralight bosonic dark matter, has received considerable attention due to the number of problems it might help to solve. Among these are the cusp-core problem and the abundance of small structures of the standard cold dark matter model. In this talk, we show that multi-state solutions of the Gross-Pitaevskii-Poisson equations, interpreted as galactic...
We consider gravitational collapse of a spherically symmetric sphere of a fluid with spin and torsion into a black hole. We use the Tolman metric and the Einstein-Cartan field equations with a relativistic spin fluid as a source. We show that gravitational repulsion of torsion prevents a singularity and replaces it with a nonsingular bounce. Quantum particle production during contraction...
The wide debate on foundational issues in quantum mechanics, which took place at the famous 1957 Chapel Hill conference on “The Role of Gravitation in Physics”, is here critically analysed with an emphasis on Richard Feynman's contributions [1, 2, 3]. One of the most debated questions at Chapel Hill was whether the gravitational field had to be quantized at all and its possible role in wave...
Soft Gamma-Ray Repeaters and Anomalous X-ray Pulsars (SGR/AXPs) are isolated compact stars identified due to a characteristic quiescent soft X-ray emission as well as bursts events. They can also emit in other energy ranges, from radio up to hard X-rays. Their nature is still a question for debate, and several emission mechanisms have been proposed, such as neutron star (NS) with a...
We propose a cosmological model that can provide a common origin to several of the anomalous features observed at large angular scales in the cosmic microwave background (CMB). More concretely, we show that a power suppression, a dipolar asymmetry, and a preference for odd-parity correlations, with amplitude and scale dependence in consonance with observations, are expected from this scenario....
Models of the evolution of stars with initial masses of approximately $80 - 240 M_\odot$ include instability due to the production of electron positron pairs in some portion of the star. The resulting supernovae do not leave behind a black hole remnant, meaning that no black holes in the mass range $50-120 M_\odot$ are expected to form. However, a fundamental assumption in these models is that...
Future gravitational wave detectors will map out and characterize every binary merger in the history of the universe. The possibilities for new and unexpected scientific discoveries from this wealth of data is staggering, but hinges crucially on complementary advances in our theoretical understanding of the nature of gravitational wave sources. However, the path from Einstein’s equation to...
We show that spinors propagating in curved gravitational background
acquire an interaction with spacetime curvature, which leads to a
quantum mechanical geometric effect. This is similar to what happens
in the case of magnetic fields, known as the Pancharatnam-Berry phase.
As the magnetic and gravitational fields have certain similar
properties, e.g. both contribute to curvature, this...
We investigate the influence of the chimney topology TxTxR of the Universe on the
gravitational potential and force that are generated by point-like massive bodies. We obtain three distinct expressions for the solutions. One follows from Fourier expansion of delta functions into series using periodicity in two toroidal dimensions. The second one is the summation of solutions of the Helmholtz...
In 2019, the Event Horizon Telescope published the first image of a black hole, paving the way for future efforts to improve our understanding of emission around compact objects. However, many of the most prominent and unexpected effects of black holes on their images are only visible at extremely fine resolutions. To analyze these features, I will describe an approach to adaptive ray-tracing...
Gravitational tidal forces conceal very interesting effects when combined with the extended nature of the wavefunction of a freely-falling quantum particle. The reason being that inertial properties of the particle get then mixed with the gravitational effects in such a way that, as in classical mechanics, the ratio of the gravitational mass to the inertial mass of the particle emerges in an...
First proposed in 1964 by Sjur Refsdal, gravitational lensing provides a straightforward and elegant geometrical way of estimating the Hubble constant from cosmologically distant variable sources. The method relies on observationally determined time delays between light arriving through different multiple images, and the mass models of the lens, which are constrained by observed image...
If the number of extra dimensions is odd, the full spacetime becomes odd-dimensional and the formation of gravitational radiation is obscured by violation of the Huygens principle. Gravitational waves must travel with the speed of light, while the full retarded gravitational field of a localized source propagates with all velocities lower or equal to the speed of light. To calculate...
We analyze the scalar radiation emitted by a source in geodesic circular orbits around a Schwarzschild-de Sitter black hole. We obtain the emitted power using quantum field theory in curved spacetimes framework at tree level. We compare our results with the scalar synchrotron radiation in Schwarzschild spacetime.
Possible interactions of dark matter (DM) with Standard Model (SM) particles can be tested with spectral distortions of the cosmic microwave background (CMB). In particular, a non-relativistic DM particle that scatters elastically with photons, electrons or nuclei imprints a negative chemical potential μ to the CMB spectrum, as I will explain in this talk. I will show how this effect can be...
The spectrum of ringdown waves which terminates the gravitational waveform of binary black hole merger contains information about both the properties of the merger’s remnant black hole, as well as the geometry of the system as it enters its final plunge and merger. This suggests that measurements of the ringdown spectrum could teach us about a binary’s geometry, provided we know how to invert...
Precision measurements of isotope shifts could reveal new physics beyond the Standard Model. Measurements of these shifts for two transitions in at least three pairs of isotopes for a given element allows the construction of a so-called King plot, where deviations from linear behaviour could point to a previously unknown boson mediating a fifth fundamental force that couples electrons to...
Over the last 5 years, the amount of data we have about Fast Radio Bursts has grown at a rapid, indeed accelerating rate. The next 5 years promises to bring even more data and, with it, the opportunity to really tackle some key questions both in our understanding of FRB physics and of the Universe on large scales. In this talk we will focus on the role FRBs may play as tools of discovery and...
In this talk we present how the Newtonian force of gravity of a central field corresponds exactly to the force experienced by a stationary observer in Schwarzschild spacetime. This exercise does not require any approximation nor further assumptions and relies solely in the geometrised Newton's second law.
The paradigm of slow-roll inflation provides a snapshot of the early universe that is in good agreement with present observations. Despite its success, most of the models studied so far rely heavily on the assumption that the universe is perfectly isotropic at early times. In this talk, I will discuss recent advances in anisotropic inflationary models. We adopt a Fock quantization for...
Alternative theories of gravity and the parameterized deviation approach allow black hole solutions to have additional parameters beyond mass, charge and angular momentum. Matter fields could be, in principle, affected by the additional parameters of these solutions. We compute the absorption cross section of massless spin-0 waves by static Konoplya-Zhidenko black holes, characterized by a...
The CNO cycle consists of a series of nuclear reactions that provide energy in stars. There exist multiple different cycles depending on temperature and relative abundance of elements in stars. In the Sun the CNO cycle is a catalyst cycle where nuclear reactions cycle through carbon, nitrogen and oxygen. Initially, a free proton fuses with a carbon-12 nucleus starting a sequence of reactions...
Scalar-tensor theories enjoying a shift symmetry can describe black holes with scalar hair. I will discuss which of these theories can give rise to acceptable black holes with hair, based on three requirements. These are stability under generic perturbations, consistency from the point of view of effective field theory, and the existence of a standard UV completion.
I will argue that in the...
The first mention of a (Newtonian) BH dates back to 1783, when Michell presented a model of a massive “Dark Star”, trapping light particles on its surface. The Schwarzschild solution from 1916 entailed two singularities – at the origin and at the Schwarzschild radius; their interpretation has been subject of an intense debate over the 20s-30s. Einstein argued that particle orbits lower than...
In this talk we will review the known result that the background evolution of standard LQC can be reproduced by a covariant metric-affine f(R) theory all the way up to bounce curvatures. We will then show that other Loop Cosmologies dubbed as mLQC-I and mLQC-II, differing on standard LQC due to quantisation ambiguities related to the Lorentzian term of the Hamiltonian, also admit covariant...
The idea that dark matter could be made of stable relics of microscopic black holes is not new. In this article, we revisit this hypothesis, focusing on the creation of black holes by the scattering of trans-Planckian particles in the early Universe. The only new physics required in this approach is an unusually high-energy scale for inflation. We show that dark matter emerges naturally and we...
Two mechanisms of gravitational waves (GWs) emission in fast-spinning white dwarfs (WDs) are investigated: accretion of matter and magnetic deformation. In both cases, the GW emission is generated by an asymmetry around the rotation axis of the star. However, in the first case, the asymmetry is due to the amount of accreted matter on the magnetic poles, while in the second case it is due to...
Within the formalism of General Relativity it is possible to operationally define or characterize a distinguished clock and time. This is the so-called standard clock providing proper time. Also within Quantum Mechanics it is possible to define a clock and the corresponding time. This clock is an atomic clock and it provides time in the unit of the second. Both clocks are compatible though...
With the success of the ESA Planck mission, the concordance cosmological models is established as the reference framework. However, outstanding questions about this model are still unanswered. In particular the simplest inflationary model proposed as the origin of the initial matter perturbations is favoured by Planck measurement of the spectral index and low non-Gaussianity. Nevertheless, it...
The cores of (sub)giants rotate much slower than expected from known hydrodynamic braking mechanisms. Magnetic torques generated by differential rotation are potentially much more effective. I'll briefly review magnetorotational and Tayler instabilities, which in their current versions are also insufficient. A big problem facing improvement are a number of critical surprises encountered in...
Compact astrophysical objects such as neutron stars (NSs) offer natural laboratories that can accrete sizable amount of Dark Matter (DM) in extreme density regimes. In this work, we study the presence of self-interacting bosonic DM in NSs through its effect on various properties of NSs. In our scenario, the bosonic DM and baryonic matter (BM) are mixed together which are interacting only...
The highly-redshifted 21 cm line of neutral hydrogen holds great promise for cosmology. Observing this signal, however, is exceedingly challenging. Experiments must contend with the signal's inherent faintness, overwhelmingly bright astrophysical foregrounds, human-generated radio interference, and the Earth's own ionosphere. And, these challenges are all exacerbated for experiments looking...
Using Newman-Penrose formalism in tetrad and spinor notation, we perform separation of variables in the wave equations for massless fields of various spins s=1/2, 1, 3/2, 2 on the background of exact plane-fronted gravitational wave metrics. Then, applying Wald's method of adjoint operators, we derive equations for Debye potentials generating these fields and find inverse projection operators...
The Hubble constant (H0) tension between Type Ia Supernovae (SNe Ia) and Planck measurements ranges from 4 to 6 σ. To investigate it, we estimate H0 in the ΛCDM and w0waCDM models by dividing the Pantheon sample, a collection of 1048 SNe Ia, into 3, 4, 20, and 40 bins. A preliminary consistency check is performed, considering the compatibility of contours for 3 and 4 bins with the ones of the...
Asymptotically flat spacetimes are known to possess an infinite number of symmetries known as the Bondi-Metzner-Sachs (BMS) supertranslations. These BMS symmetries were shown to be related, both, to the gravitational memory effect and Weinberg’s soft theorems, the significance of which was recently realised by Hawking et. al. who conjectured that applying these relations to an asymptotically...
Betelgeuse, a bright star in the shoulder of the Orion constellation has
been known for centuries - even appearing in drawing on the walls of the Lascaux Caves in Southwestern France. And an unexpected amazing phenomenon occurred
last year.
The bright cool supergiant Betelgeuse became historically faint in
February 2020. Various explanations have been offered for its
unusual behavior...
With the recent direct observation of gravitational waves, a new avenue of observing the Universe has become available. As a result, much effort is being devoted to the design of new detectors sensitive to different gravitational wave sources. One unique proposal is to detect gravitational waves using a Bose-Einstein Condensate (BEC) by using quantum metrology.
In this talk, I will show that...
Magnetic fields, if present in the plasma prior to last scattering, would induce baryon inhomogeneities and speed up the recombination process. As a consequence, the sound horizon at last scattering would be smaller, helping to relieve the Hubble tension and the S8 tension. Intriguingly, the strength of the magnetic field required to alleviate the Hubble tension happens to be of the right...
Using effective field theory methods, we calculate the 5PN
potential corrections to the binary black hole system, also
including the tail terms, except the purely rational terms of
O(\nu^2). Comparisons are made with the literature. The
contributions of O(\pi^2 \nu^2) are calculated for the first
time. We provide the Hamiltonian for harmonic...
We analyze the rotation curves that correspond to a Bose--Einstein Condensate (BEC) type halo surrounding a Schwarzschild--type black hole to confront predictions of the model upon observations of galaxy rotation curves. We model the halo as a BEC in terms of a massive scalar field that satisfies a Klein--Gordon equation with a self--interaction term. We also assume that the bosonic cloud is...
In the framework of reduced phase space Loop Quantum Gravity (LQG), we propose a new approach in coherent state path integral formulation which allows the spatial cubic lattice (graph) to change dynamically in the physical time evolution. The equations of motion of the path integral derive the effective dynamics of cosmology from the full LQG, when we focus on solutions with homogeneous and...
We show that in absence of entropy or effective anisotropic stress the freedom in the choice of the initial energy scale of inflation implies the existence of an infinite family of dual slow-roll parameters histories which can produce the same spectrum of comoving curvature perturbations. This implies that in general there is no one-to-one correspondence between the spectrum and higher order...
Here I share my experience in communicating some knowledge from relativistic astrophysics and associated Einsteinian physics in a scientific novel, named Blue Infinity, which I’ve written one year ago. What is special when we try to transmit the scientific truth through fictional characters representing researchers and students working in real scientific centers?
A certain type of matter with anisotropic pressures can add to the Reissner-Nordström metric a term proportional to a power of the radial coordinate. Using the standard method of separating variables for the Hamilton-Jacobi equation, we study the shadow of the corresponding rotating solution, obtained through the Newman-Janis algorithm. We define and calculate three observables in order to...
Mass and radius constraints of compact stars (CS), i.e. Neutron stars (NS) and White Dwarfs (WD), based on electromagnetic data are challenging. Radius measurements are mainly based on observation of thermal emission and comparison with theoretical models. Modeling, however, due to the complex and relativistic nature of compact objects, suffers from a number of complications such as parameter...
To avoid ambiguity in the phase readout, optical clock measurements are constrained to operate with an interrogation time that is short enough that the accumulated optical local oscillator (OLO) phase wander remains within ±π/2 radians. This constraint, known as the coherence limit, has motivated a variety of techniques to allow interrogations beyond this limit. A recent proposal has been put...
We study asymptotically flat black holes with massive graviton hair within the ghost-free Bigravity theory. There have been contradictory statements in the literature about their existence: such solutions were reported some time ago, but later a different group claimed the Schwarzschild solution to be the only asymptotically flat black hole in the theory. We have analyzed the issue ourselves...
The largest amount of antineutrinos detected about the Earth is emitted by the natural radioactive decays inside the Earth: more than 99% of the present-day Earth’s radiogenic heat is originated by the β$^{-}$ decays of $^{40}$K and of $^{232}$Th and $^{238}$U chains isotopes. Other flux components are provided by cosmic rays interactions in the atmosphere or by possible extra-terrestrial...
In 1911 Einstein proposed that light-bending by the Sun's gravitational field could be measured during a total solar eclipse. The first opportunity in which this measurement would be tried, was during the total solar eclipse of October 10, 1912. We report about the expeditions sent to Brazil to observe this eclipse, including the one from the Córdoba Observatory, from Argentina, which aimed to...
The way we experience time is in the accumulation of experiences and events that happen in the moment, and then are behind us. Since the time of Anaximander at least; philosophers have tried to explain both the nature of time and its origin or basis. In modern times; scientists are the ones exploring the domain of time, so now they attempt to explain the nature and basis of time – with varying...
Note, that micro black holes last within micro seconds, and that we wish to ascertain how to build, in a laboratory, a black hole, which may exist say at least up to 10^−1 seconds and provide a test bed as to early universe gravitational theories. First of all, it would be to determine, if the mini black hole bomb, would spontaneously occur, unless the Kerr-Newmann black hole were carefully...
In this talk we focus on weak inhomogeneous Universe models at low redshift, described by the Lemaître-Tolman-Bondi (LTB) metric within the framework of f(R) modified gravity theories. The principal aim of this study was to compare the evolution of inhomogeneous perturbations in the ΛCDM and alternative f(R) cosmological models, assuming a flat Friedmann-Lemaître-Robertson-Walker (FLRW) metric...
Free massless fields of any spin in flat D-dimensional spacetime propagate at the speed of light. But the retarded fields produced by the corresponding point-like moving sources share this property only for even D. Since the Green’s functions of the d’Alembert equation are localized on the light cone in even-dimensional spacetime, but not in odd dimensions, extraction of the emitted part of...
We present a fully relativistic framework to evaluate the impact of stochastic inhomogeneities on the prediction of the Hubble-Lemaitre diagram. To this aim, we relate the fluctuations of the luminosity distance-redshift relation in the Cosmic Concordance model to the intrinsic uncertainty associated to the estimation of cosmological parameters from high-redshift surveys (up to z = 4). We...
Orientability is an important topological property of spacetime manifolds.
It is generally assumed that a test for spatial orientability requires a journey
across the whole 3-space to check for orientation-reversing paths.
Since such a global expedition is not feasible, theoretical arguments that combine
universality of physical experiments with local arrow of time, CP violation and...
In this work, we investigate the structure, the radial stability, pycnonuclear reaction and inverse $\beta$-decay in white dwarfs with a finite temperature. Regarding the matter within hot white dwarfs, we consider that it is composed of nucleons and electrons confined in a Wigner-Seitz cell surrounded by free photons. Since photons are being considered, in order to connect smoothly the...
Gravitational shockwaves are simple exact solutions of Einstein equations representing the fields of ultrarelativistic sources and idealized gravitational waves (shocks). Historically, much work has focused on shockwaves in the context of possible black hole formation in high energy particle collisions, yet they remain at the forefront of research even today. Representing hard modes in the...
In a brief review, we draw attention to the “hypercomplex medium” with the accent on quaternion (Q) algebra and contiguous areas: biquaternion (BQ) numbers, Q-spinors, and related groups. Due to Heaviside-&-Gibbs’ vector algebra, this “Q-set” was nearly abandoned in XX century rarely emerging as a math tool [1]. However, it turns out to contain many geometric images and equations related to...
Astrophysical problems such as modelling of core-collapse supernovae, collapses of protostellar clouds as well as other processes, involving collapsing matter, deal with regions (e.g. protostars, protoneutron stars), where a speed of sound has much larger values, than in remaining parts of a computational domain. A time-step in explicit numerical schemes, thus, has to be bounded according to...
Obsolete scientific concepts are embedded in school primary school education. This means that the large majority of people who do not study specialised physics beyond middle school are barely exposed to modern scientific concepts. Moreover they lack the language of modern science and hence are entirely disenfranchised when it comes to science policy on issues such as climate change, 5G mobile...
The HAWC gamma-ray observatory has discovered very extended TeV gamma-ray structures around two pulsars Geminga and B0656+14. The gamma-ray emission, with its size of tens of parsecs, is produced from high-energy electrons and positrons around these two nearby middle-aged pulsars. Morphology studies suggest that the diffusion in the vicinity of these two pulsars is 100 times slower than the...
The properties of light are premises in the foundations of modern physics: they were used to derive special and general relativity and are the basis of the concept of time and causality in many alternative models. Therefore, it is worthwhile to study the back-action of light on the gravitational field with its rich phenomenology, even though the effects are in general very weak. In this talk,...
The isolated formation channel is one of the most studied formation scenarios for stellar mass black hole binary (BBH) mergers detected by LIGO and Virgo. Focusing on the effects of
uncertain stellar and binary physics, we investigate this BBH formation channel using the rapid binary population
synthesis code SeBa.
Regardless of our assumptions, the two must common formation path within...
Einstein’s general relativity predicts that a gravitational wave is allowed to have two polarizations called tensor-mode: plus and cross modes. On the other hand, the general metric theory of gravity predicts that a gravitational wave is allowed to have up to six polarizations: two scalar and two vector modes in addition to tensor modes. In case the number of laser-interferometric...
In the so-called Ricci-based Gravity theories (RBGs for short) it is possible to transform a modified gravity problem into a standard problem in GR coupled to a modified matter source. Taking advantage of this property, one can also take non-vacuum solutions of GR and use them as seeds to generate new solutions in other theories of the RBG family. I will present recent results in this...
What do archival observations tell us about the M87 black hole?
With the 2017 observations of the Event Horizon Telescope we observed the M87 supermassive black hole with linear resolution corresponding to about 3 Schwarzschild radii, revealing a bright ring surrounding dark center – a feature dubbed a “black hole shadow”. Several archival observations of M87 with the EHT prototype...
The recent analysis of gravitational wave data by the Ligo-Virgo collaboration (arXiv:2010.14533) provides evidence of merging binary black holes with non-zero spins.
Spinning binary BHs with aligned spins can result from the tidal spin-up of a Wolf-Rayet binary that survived the common envelope phase. However, tidal spin-up results in spins aligned with the orbital angular momentum, a...
We review various theoretical models and scenarios based on teleparallel gravity and torsional modifications of gravity. Then we apply them in a cosmological framework, discussing the early and late time solutions as well as the observational constraints using various datasets. Finally we present the recent possibility of using multi-messenger astronomy, in order to investigate torsional...
Combining information from the first gravitational wave detected gamma-ray burst, GRB 170817 with observations of cosmological GRBs holds important lessons for understanding the structure of GRB jets and the required conditions at the emitting region. It also re-frames our understanding of more commonly observed phenomena in GRBs, such as X-ray plateaus, and sets our expectations for future...
The CRESST-III (Cryogenic Rare Event Search with Superconducting Thermometers) experiment, located in the Gran Sasso underground laboratory (LNGS, Italy), aims at the direct detection of light dark matter (DM) particles.
Scintillating CaWO$_4$ crystals operated as cryogenic detectors at mK temperatures are used as target material for elastic DM-nucleus scattering. The simultaneous...
The accelerated expansion of the universe demands presence of an exotic matter, namely the dark energy. Though the cosmological constant fits this role very well, a scalar field minimally coupled to gravity, or quintessence, can also be considered as a viable alternative for the cosmological constant. We study $f(R)$ gravity models which can lead to an effective description of dark energy...
Short GRBs are unique tools that allow us to study binary neutron star (NS) mergers across all cosmic times. The study of short GRBs at high redshifts is particularly important as it allows us to estimate the typical lifetime of their progenitors, and whether they merged early enough to enrich the universe with heavy elements. In this contribution I will review the high-energy properties of...
Sources of high-energy, dense and collimated photon and lepton beams enable new avenues for research in strong-field QED and relativistic laboratory astrophysics [1]-[2].
Here we show that a high-current ultrarelativistic electron beam interacting with multiple thin conducting foils can undergo strong self-focusing accompanied by efficient emission of gamma-ray synchrotron photons....
Gravitational lensing is a widely used probe in the study of the dark universe. Besides the gravity, the free electrons in the plasma can also cause deflections of the light. Although plasma lensing has a distinct similarity to gravitational lensing, particularly in its mathematical description, plasma lensing introduces additional features, such as wavelength dependence, diverging deflection,...
A semiclassical state is studied as it approaches a cosmological Bianchi II singularity, by means of the evolution of its moments. Classically this system undergoes a transition between two Bianchi I models, with a specific and well-known transition law, which is derived based on the conservation of certain physical quantities. In the quantum theory, however, these constants of motion are...
The phenomenological waveform modelling program is one of the main approaches to accurately model gravitational wave signals from compact binary coalescences during all the emission stages, incorporating information from several analytical and numerical frameworks (Post-Newtonian theory, Numerical Relativity, Black-hole perturbation theory) in compact close-form computationally efficient...
Ultraluminous X-ray sources (ULXs) are very bright, off-nuclear, point sources with luminosity exceeding the standard Eddington limit of a stellar-mass black hole (BH). The existing physical scenarios to explain their unusual large luminosity and spectral nature are either super-Eddington accretion around a stellar-mass BH or the existence of the missing class of intermediate-mass BH (IMBH)....
Magnetic fields play an important role in the dynamics of binary neutron star mergers and on their gravitational wave and electromagnetic emission (such as the production of relativistic jets and short gamma-ray bursts). In this talk I will review some of the main results in the field of fully general relativistic magnetohydrodynamic (GRMHD) simulations of these systems focusing in particular...
Based on our recent results we present the complete class of vacuum solutions in the Einstein–Gauss–Bonnet gravity which admit non-expanding, shear-free and twist-free null geodesic congruence and thus form the Kundt family of geometries. We explicitly derive the field equations and classify their solutions into three distinct subfamilies. Algebraic structure of the curvature tensors is...
The CDEX program pursues the direct detection of light dark matter candidates with an array of germanium detectors since 2009 at the deepest operating underground site located in Sichuan, China. Searches of modulation effect of light WIMPs[1], WIMPs-nucleus interaction via Midgal effect[2], dark photon model[3], solar axions and axion-like particles[4] as well as the...
As the gravitational-wave interferometers increase their sensitivity, they detect an ever larger number of compact binary coalescences: a small but significant fraction of which contains detectable higher multipoles in addition to the dominant (2, 2) mode. Such higher multipoles can be identified with a minimally-modeled extension of the coherent WaveBurst (cWB) burst pipeline.
During the...
Many short Gamma-Ray Bursts (sGRBs) have a prolonged plateau in the X-ray afterglow lasting up to tens of thousands of seconds. A central engine injecting energy into the remnant may fuel the plateau. We develop a simple analytic model which naturally produces X-ray plateaux using a magnetar as the central engine. Our model leverages well-established descriptions of young supernova remnants...
Analytical expressions are obtained for four tensors of kinetic coefficients from the solution of the Boltzmann equation by the Chapman-Enskog method in the 3-polynomial approximation, taking into account electron-electron collisions for the case of nondegenerate electrons in a magnetic field.
For strongly degenerate electrons, asymptotically accurate analytical expressions for the thermal...
The Crab Pulsar's radio emission is unusual, consisting predominantly of giant pulses, with durations of about a micro-second but structure down to the nano-second level, and brightness temperatures of up to $10^{37}\,$K. It is unclear how giant pulses are produced, but they likely originate near the pulsar's light cylinder, where corotating plasma approaches the speed of light. We report...
A class of modified gravity theories with higher order derivative terms of a function of the matter Lagrangian $f(L_m)$ is considered. We will consider the Newtonian limit of the theory and show that the model predicts the standard Poisson equation for a massive test particle due to the higher order nature of the derivative matter coupling. Generally the energy momentum tensor is not...
We check the dynamical and observational features of four typologies of logotropic dark energy models, leading to a thermodynamic cosmic speed up fueled by a single fluid that unifies dark energy and dark matter. We first present two principal Anton-Schmidt fluids where the Gruneisen parameter is free to vary and then fixed to the special value We also investigate the pure logotropic...
The vacuum instability effect (the Schwinger effect) in an asymmetric electric field of an analytic form is studied nonperturbatively representing a so-called exactly solvable case. Among t-electric potential steps that belong to exactly solvable cases (Sauter-like electric field, T-constant electric field, exponentially increasing and exponentially decreasing electric field, and inverse...
Measuring dark matter (DM) signals via electron recoil provides an important means
for the direct detection of light DM particles. In this talk, I will show that the recent XENON1T anomaly with electron recoil energy around (2 − 3) keV can be naturally explained by the exothermic inelastic scattering between DM and electrons in a 2-component DM scenario. The stability of the heavier component...
The process of choosing appropriate educational content to teach Einsteinian physics in middle school is a challenge for researchers and teachers. The Einstein-First project in Australia is designing and implementing an Einsteinian physics curriculum for schools. My research is designed to trial a learning progression of Einsteinian concepts within an overall curriculum structure for year 7....
In this talk, we discuss the extended gravitational decoupling approach for a static sphere in the framework of f(R,T) gravity where R represents the Ricci scalar and T is the trace of the energy-momentum tensor. In this approach, the domain of a known solution is extended by incorporating a new gravitational source. Transformations in radial and temporal metric functions split the system of...
In the era of multi-messenger astrophysics, binary neutron star (BNS) mergers have proven to be one of the prime sources of gravitational waves (GWs), also able to produce short-gamma ray bursts (SGRBs) as well as radioactively powered kilonovae. General relativistic magnetohydrodynamic (GRMHD) simulations represent a fundamental tool to probe the underlying physical mechanisms involved in...
The dark matter direct detection rates are highly correlated with the phase space distribution of
dark matter particles in our galactic neighbourhood. In this paper we make a systematic study of the
impact of astrophysical uncertainties on electron recoil events at the direct detection experiments
with Xenon and semiconductor detectors. We find that within the standard halo model there...
Newly-born millisecond magnetars are competing with black holes as source of the gamma-ray burst (GRB) power. In ten years of activity, Swift has provided compelling but indirect evidences supporting the magnetar central engine for both long and short GRBs, that is currently the best way to interpret several correlations observed between prompt and afterglow properties. We review the main...
We investigate strong-field gravitational lensing by rotating Simpson-Visser black hole, which has an additional parameter ($l$), apart from mass ($M$) and rotation parameter ($a$). It can admit Cauchy and event horizons for some parameters and free from the singularity and assess phenomenological differences from the Kerr black holes. We also find a decrease in the deflection angle...
The recent observing run of Advanced LIGO and Virgo was fruitful in gravitational-wave (GW) detections and the observation of GW190521 is one of the most important discoveries. With a remnant black hole of about 140 solar masses, this is the first strong evidence for the existence of intermediate-mass black holes that are heavier than stellar mass and lighter than supermassive black holes. In...
We consider crossed electric and a magnetic fields $\left(\vec{B}=B\hat{z},~\vec{E}=E\hat{y}\right)$, with $E/B<1$, in presence of some initial number of $e^{\pm}$ pairs. We do not discuss here the mechanism of generation of these initial pairs. The electric field accelerates the pairs to high-energies thereby radiating high-energy synchrotron photons. These photons interact with the magnetic...
We analyze the Bianchi I cosmology in the presence of a massless scalar
field and describe its dynamics via a semiclassical and quantum polymer
approach. We investigate the morphology of the emerging Big Bounce
by adopting three different sets of configurational variables:
the natural Ashtekar connections, the Universe volume plus two anisotropy
coordinates and a set of anisotropic volume-like...
Abstract:
We attempt to address the old problem of accretion flow: the origin of turbulence and hence transport of angular momentum in accretion flows. We undertake the problem by introducing an extra force in Orr-Sommerfeld and Squire equations along with the Coriolis force mimicking the local region of the accretion disk. Subsequently, we solve the equations with the WKB approximation...
Magnetars are slowly rotating, young, and isolated neutron stars with surface dipole magnetic fields exceeding the quantum electrodynamic magnetic field limit. They exhibit highly energetic behavior, as in the case of soft-gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs). Recently, they have been studied with paramount interest by almost every modern X-ray telescope. Despite the...
The possibility to detect gravitational waves (GW) from planetary-mass primordial black hole (PBH) binaries with electromagnetic (EM) detectors of high-frequency GWs is investigated. We consider two patented experimental designs, based on the inverse Gertsenshtein effect, in which incoming GWs passing through a static magnetic field induce EM excitations inside either a TM cavity or a TEM...
Modern science understanding depends on fundamental mathematical areas that go beyond primary school arithmetic. One of Einstein-First's goals is to create seamless learning progressions that begin in early primary school, designed to ensure that everyone develops an intuitive understanding of mathematical concepts and ideas that allow us to comprehend everything from the reality around us to...
The first neutron star-neutron star merger (NS-NS: GW170817) was detected in gravitational waves by LIGO/Virgo in a galaxy in which the majority of star formation was taking place a long time ago (∼11 Gyr). Only some extreme evolutionary models (with small NS natal kicks and high common envelope efficiency) can generate NS-NS merger rates in old host galaxies consistent with the LIGO/Virgo...
The goal of this talk is to present a conjecture which states that the proper-time series expansion of the one-loop effective Lagrangian of quantum electrodynamics can be partially summed in all terms containing the field-strength invariants $\mathcal{F} = \frac{1}{4} F_{\mu\nu}F^{\mu\nu} (x)$, $\mathcal{G}= \frac{1}{4} \tilde F_{\mu\nu}F^{\mu\nu}(x)$, including those that also have ...
With the increasing sensitivities of the gravitational wave (GW) detectors and more detectors joining the international network, the chances of detection of a stochastic GW background (SGWB) is progressively increasing. Different astrophysical and cosmological processes are likely to give rise to backgrounds with distinct spectral signatures and distributions on the sky. The observed...
A photon region in the black holes gravitational field is defined as a compact region where photons can travel endlessly without going to infinity or disappearing at the event horizon. In the Schwarzschild metric, the photon region degenerates to the photon sphere which is a three-dimensional umbilic hypersurface in spacetime (its second quadratic form is proportional to the induced metric)....
After 15 years of Swift observations, the knowledge of the class of short GRBs experienced an impressive boost. The discovery of short GRB afterglows in 2005, provided the first insight into their energy scale, environments and host galaxies. The lack of detection of associated supernovae proved that their progenitors are not massive stars. The spectacular detection of the first...
In this work we study an "ungravity" origin to the cosmological constant. We derive the modified Friedmann equations from the first law of thermodynamics and the "ungravity" entropy-area relationship. From the modified Friedmann equations (in the late time regime) we find an effective cosmological constant.
Many new physics models like SUSY can have dark matter candidates. Collider experiment provides a unique approach search for dark matter candidates. Like neutrinos, dark matter candidates, once produced from high energy particle collisions, would escape from detection and leave a signature of missing energy. The production mechanism through effective field theory model, simplified model and...
We investigate radiation from asymptotic zero acceleration motion where a horizon is formed and subsequently detected by an outside witness.
Many neutron stars propagate through the interstellar medium with supersonic velocities, and their magnetospheres interact with the interstellar medium (ISM), forming bow shocks and magnetotails.
Using numerical MHD simulations, we investigated the propagation of a magnetized neutron stars through a non-uniform ISM, the interaction of the magnetospheres with the ISM and the influence of ISM...
Doran horizon penetrating coordinates are adopted to study specific perfect MHD processes around a Kerr black hole, focusing in particular on the physical relevance of selected electrodynamical quantities.
In most cases the TOV equation appears as the relativistic counterpart of the classical condition for hydrostatic equilibrium, and characterises the static equilibrium of bound, spherical distributions of matter such as stars. In the present work we aim at showing that a generalised TOV equation also characterises the equilibrium of models endowed with other symmetries besides spherical. We...
In this talk I will discuss the possibility to extend the notion of the Nieh-Yan topological invariant to generic metric-affine geometries, where both torsion and nonmetricity are taken into account. Notably, the properties of projective invariance and topologicity can be independently accommodated by a suitable choice of the parameters featuring this new Nieh-Yan term. Considering a special...
I will discuss supernovae associated with gamma-ray bursts and what they tell us about the progenitors of gamma-ray bursts. I will focus on the supernova diversity from gamma-ray bursts and what the diversity tells us.
We present a purely geometric method for constructing a rank two Killing tensor in a spacetime with a codimension one foliation that lifts the trivial Killing tensors from slices to the entire manifold [1]. The resulting Killing tensor can be nontrivial. A deep connection is found between the existence of such a Killing tensor and the presence of generalized photon surfaces in spacetime with...
A scenario for the formation of an isolated X-ray pulsar 1E161348-5055 with an anomalously long period of 6.7 hours is proposed. It is shown that this pulsar can be a descendant of a massive X-ray binary system, which disintegrated about 2000 years ago after a supernova explosion caused by the core collapse of a massive component. X-ray radiation of this object in the present epoch is...
Tens of binary black hole (BH) mergers and a few binary neutron star (NS) mergers have been observed by LIGO/Virgo gravitational wave detectors, strongly advancing our understanding of the lives and deaths of compact objects. Recent realistic globular cluster simulations have shown that dynamical formations of binary BHs can entirely explain the observed rate of binary BH mergers. At the same...
The low-mass X-ray binary Scorpius X-1 (Sco X-1) is a promising source of continuous gravitational waves for ground-based detectors. We use an improved method to search for signals with nearly constant frequency from Sco X-1 in the range of 40-180 Hz in LIGO O2 public data. Thanks to the efficiency of the search pipeline we can use a long coherence time and significantly improve the...
CGHS black holes have rightfully garnered much attention over the last few decades as the models are simplified (1+1)-dimensional versions of black hole evaporation. Their solubility has lead to tractable physical insights into the radiative process. Concurrently, moving mirrors are well-known simplified (1+1)-dimensional models for black hole evaporation. We synthesize the two by finding an...
Accelerated charges emit electromagnetic radiation and the consequent energy-momentum loss alters their trajectory. This phenomenon is known as radiation reaction and the Landau-Lifshitz (LL) equation is the classical equation of motion of the electron, which takes into account self-consistently radiation-reaction effects in the electron trajectory. By using the analytical solution of the LL...
The spacetimes with the NUT parameter are commonly associated with an unwanted defect in the form of a singular axis of symmetry. In the case of the Taub-NUT spacetime the most common remedy is the Misner’s interpretation: by compactifying the orbits of the cyclic time symmetry one discovers that the spacetime has a structure of the Hopf fibration. Then Taub-NUT may be regarded as a smooth...
The DArk Matter Particle Explorer (DAMPE) is a satellite-borne, calorimetric type, high-energy-resolution space cosmic ray and gamma-ray detector. It was launched in December 2015 and has been stably operating for more than five years. Its three major scientific objectives are dark matter indirect detection, cosmic ray physics and gamma-ray astronomy. Precise measurements of the all-electron,...
We present a unified formulation of geometrical optics in General Relativity. Consider two causally connected, locally flat neighborhoods. Suppose that each null geodesic originating in one neighborhood terminates at the other one, and the curvature along the trajectory is small enough, such that the linear geodesic deviation equation holds. Also, let the observation be performed by a number...
The elastic crust of a neutron star fractures repeatedly as it spins down electromagnetically. An idealized, macroscopic model of inhomogeneous crustal failure is presented based on a cellular automaton with nearest neighbor tectonic interactions involving strain redistribution and dissipation.
Predictions are made of the size and waiting-time distributions of failure events, as well as the...
In this talk we will argue that, in generic metric-affine theories of gravity, non-linear $R_{(\mu\nu)}$ terms in the action do not introduce new degrees of freedom, but rather couple the rest of the degrees of freedom of the theory among themselves. At a perturbative level, this leads to a set of effective interactions among the matter degrees of freedom suppressed by a heavy mass scale that...
The AstroCamp is an academic excellence program in the field of astronomy and physics for students in the last 3 years of pre-university education, i.e. roughly 15-18 year olds. It was created in 2012 and is organized by CAUP and several national and international partners, and now accepts applications from 42 eligible countries. Academic activities include two courses (each with 15h of...
In the current study, we present hydrodynamical simulations and post-process radiation transfer calculations of photospheric emission in GRBs. Our simulations show that the photospheric emission can reproduce the observed correlations among the spectral peak energy, $E_p$, peak luminosity, $L_p$, and isotropic energy, $E_{iso}$, as a consequence of the viewing angle dependence. We also find...
We present a new, complementary method of pulsar timing, which explicitly tracks the evolution of the pulse frequency and frequency derivative using a hidden Markov model (HMM). The HMM incorporates both stochastic spin wandering (timing noise) and glitches.
We describe how this framework can be used to detect glitches through Bayesian model selection with minimal human intervention and low...
Gravitational wave events involving very massive neutron stars, such as
GW190425, have just started to be detected. Although typically classified as
binary neutron star mergers, the observed gravitational-wave signal is
usually not able to clearly establish a neutron-star nature of the massive
primary object in the system. Thus, a black hole--neutron star system cannot
be fully ruled...
Testing gravity on low and high energy domains is essential to reconcile primordial and late times. Focusing on local and cosmic scales, red and blue shift measures between two observers plays a crucial role. We revise their use in two distinct contexts, making use of de Sitter–Schwarzschild solution and q-metric to describe low and higher energy regimes. First, we assume de...
Strong gravity regions, like the neighborhood of black holes or neutron stars, can induce non-
minimal couplings between electromagnetic fields and gravity. In these regions, gravitational fields
behave as a non-linear medium in which the electromagnetic fields propagate. For a system of mass
M and size R, the surface potential scales as M/R. Pulsar timing array, Double pulsar...
In this presentation the white dwarf close binaries AE Aquarii and AR Sco are investigated to search for signatures of particle acceleration and associated non-thermal emission. A detailed investigation of the total Fermi-LAT data base reveal signatures of pulsed gamma-ray emission in AE Aquarii, which mimics earlier reports of transient burst-like pulsed TeV gamma-ray emission reported from...
Recently, a considerable amount of attention has been given to the search for ultralight dark matter by measuring the oscillating length changes in the arm cavities of gravitational wave detectors. Although gravitational wave detectors are extremely sensitive for measuring the differential arm length changes, the sensitivity to dark matter is largely attenuated, as the effect of dark matter is...
The broadband afterglows of gamma-ray bursts provide a wealth of information vital for interpreting these extremely energetic events: the progenitor systems, the hydrodynamics of the GRB, the microphysics of relativistic shocks, and more. A proper understanding of afterglows may even allow GRBs to extend the cosmic distance ladder. However, our interpretation of afterglows is shaped by the...
In this report, we evaluate the performance of the proposed Euro-Asian network (EAN) of gravitational wave (GW) interferometers, which is planned taking into account the location of one of the detectors at the RAS Novosibirsk Scientific Center. EAN is formed by four detectors: VIRGO, KAGRA, LIGO India and Novosibirsk. The efficiency of this configuration is calculated based on typical...
We study the motion of a particle in the Bogoslovsky-Finsler space-time, where a Lorentz violation takes place due to a non-zero continuous parameter in the action. We demonstrate that the broken Lorentz symmetries are substituted by a different type of symmetry. The new symmetry vectors are generators of higher order (or hidden) symmetries that are related to integrals of motion which are...
A black hole's shadow is expected to deform under the influence of an external gravitational field caused by matter present in its vicinity. This talk aims to characterise the distortion of a Schwarzschild black hole shadow due to a non-zero quadrupole moment $c_2$ by qualitatively investigating the behaviour of light rays close to the black hole horizon. In particular, the numerical...
In my talk, I will critically examine the Penrose conjecture according to which the gravitational entropy should be quantified via the Weyl curvature, with the Clifton-Ellis-Tavakol entropy being one specific realization of this proposal. In fact, I will show that in some exact inhomogeneous and anisotropic cosmological models which arise in general relativity with either closed and open...
The extended excess towards the Galactic Center (GC) in gamma rays inferred from Fermi-LAT observations has been interpreted as being due to dark matter (DM) annihilation. In a recent paper my collaborators and I performed a new likelihood analyses of the GC and showed that when including templates for the stellar galactic and nuclear bulges, the GC shows no significant detection of a DM...
BMS supertranslation symmetries are related to both the gravitational memory effect and the Weinberg’s soft graviton theorem; the significance of which was recently realised by Hawking, Perry and Strominger (HPS) who conjectured that applying these relations to an asymptotically flat spacetime with a black hole in the interior would imply the existence of an infinite number of soft hairs for...
The stellar aberration was discovered by James Bradley in 1727, and the same astronomer discovered the nutation of the Earth's axis in 1737. At the meridian line of S. Maria degli Angeli, the giant Clementine Gnomon, built by Francesco Bianchini (1662-1729) and funded by Cardinal Gianfrancesco Albani (1649-1721), elected pope on 23 november 1700 with the name of Clement XI, the effects of...
Radio pulsar glitches probe far-from-equilibrium processes involving stress accumulation and relaxation in neutron star interiors. Previous studies of glitch rates have focused on individual pulsars with as many recorded glitches as possible. In this work we analyze glitch rates using all available glitch data, including objects that have glitched never or once. We assume the glitch rate...
Accretion discs surrounding neutron stars, black stars and white dwarfs play an important role in theoretical astrophysics. Their evolution is closely connected with the magnetic field structure. Nowadays there are different approaches for studying the magnetic field and the mechanism of its growth. However, we can conclude that it is highly likely that the origin of the magnetic field of the...
Primordial black holes are black holes that may have formed in the
early Universe. Their masses potentially span a range from as low as
the Planck mass up to many orders of magnitude above the solar mass.
This, in particular, includes black holes with mass (and spin)
comparable to those recently discovered by LIGO/Virgo. These may well
be primordial in nature, which may also be true...
In this second contribution to the MG16 on Relativity's teaching, again on the meridian line of S. Maria degli Angeli, I publish the new tables of calibration of this meridian line in order to obtain a single measurement with absolute accuracy of 2-5 arcseconds. The lower limit of 2 arcsec is for winter observations with focal length of nearly 50 meters, while 5 arcsec is reached in summer...
The shadow of a 10 meters wall casted on the soccer field of the Technical Institute Galileo Ferraris in Rome, 41.878415° N, 12.454662° E coordinates WGS84 of the gnomon, is used to perform daily measure with an accuracy within a millimiter.
The gnomon's shadow, measured from the bottom and from the side of the field with a tape meter, in the best sets of measurements, presented rms below 1...
Axion dark matter can be produced by the decay of cosmic strings, leading to large amplitude, small scale density perturbations in the axion field. These perturbations for the seeds for axion ``miniclusters’’: small and dense dark matter clumps, with mass $M\approx 10^{-12} M_{\odot}$. The seeds go on to form minicluster halos via hierarchical structure formation. By comparison between the...
Advancements in the black hole shadow observations may allow us not only to investigate physics in the strong gravity regime, but also to use them in cosmological studies. We propose to use the shadow of supermassive black holes as a standard ruler for cosmological applications assuming the black hole mass can be determined independently. First, observations at low redshift distances can be...
The possibility to detect gravitational waves (GW) from planetary-mass primordial black hole (PBH) binaries with electromagnetic (EM) detectors of high-frequency GWs is investigated. We consider two patented experimental designs, based on the inverse Gertsenshtein effect, in which incoming GWs passing through a static magnetic field induce EM excitations inside either a TM cavity or a TEM...
It is known that when charged fermions gyrate in uniform magnetic field, their energy quantizes into discrete levels, called Landau levels. The problem of Landau quantization is typically solved in presence of uniform magnetic fields. Under such condition, the Landau levels are degenerate with overlapping of spin-up fermions in a lower energy level with spin-down fermions in the next higher...
We present a correlation observed in both the optical and X-ray afterglows of long duration Gamma-ray Bursts (GRBs), between the initial luminosity (measured at restframe 200s) and average afterglow decay rate. This correlation does not depend on the presence of specific light curve features and is potentially applicable to all long GRB afterglows. We explore how the correlation decay...
The Fermi-LAT collaboration presented the second gamma-ray burst (GRB) catalog covering its first ten years of operations. A large fraction of light curves (LCs) in this catalog cannot be explained by the closure relations of the standard synchrotron forward-shock (FS) model, suggesting that there could be an essential contribution from another process. Therefore, we derive the synchrotron...
We present the precanonical Hamiltonian analysis and quantization of the Palatini formulation of the teleparallel equivalent of General Relativity in vielbein variables. It leads to more sophisticated fundamental Dirac brackets than in the case of vielbein General Relativity and it naturally leads to a covariant precanonical Schroedinger equation of quantum graviity for a...
The Meridian Line of Santa Maria degli Angeli in Rome has been realized in 1700-1702 upon the will of Pope Clement XI, since when he was Cardinal, after the project of Francesco Bianchini (1662-1729) to measure with unprecedented accuracy the tropical year and the variation of the obliquity of the ecliptic.
At this Great Gnomon for the first time in the history of astronomy, the seasonal...
The sungrazing comets are a class of comets whose number significantly increased in the last 26 years, since the SOHO coronographes entered in function, at the rithm of about hundred per year.
A review in the gravitational studies on such comets, starting from Newton is presented.
Their orbital parameters suggest their grouping as related to a few parent bodies, and the pionieristic...
The direct detection of gravitational waves has triggered excitement from physicist, astrophysicists and general public alike. The first event and many that followed originated from surprisingly heavy systems, with typical masses of 30-45 solar masses, well in excess of the masses of black holes known in X-ray binary systems. How did heavy pairs of Black holes form? What do these measurements...
The majority of massive stars is born in close binary stars, and their evolution is strongly altered by their companion star. We discuss the main mechanisms of close binary interaction, and their relevance for understanding the diversity of core collapse supernovae. Binary interaction also affects, and sometimes enables, extreme events, like hypernovae, long-duration gamma-ray bursts, super...
We shall analyze three specific general-relativistic problems in which gravitomagnetism plays the important role: the dragging of magnetic fields around rotating black holes, dragging inside a collapsing slowly rotating spherical shell of dust, compared with the dragging by rotating gravitational waves (CQG 34, 205006 (2017), Phys. Rev. D 85 124003, (2012) etc). We shall also briefly show how...
The study of High Energy (HE) and Ultra-High Energy (UHE) cosmic rays is currently being driven
by new and very interesting data from both space-borne and ground-based experiments. The talk will be devoted to a review of recent observations of electrons/positrons, protons/antiprotons, and nuclei, at energies above hundreds of GeV. New techniques and mission concepts will also be briefly discussed.
It is well accepted that most long gamma-ray bursts (LGRBs) are associated with broad-line SNe-Ibc. There is a broad consensus that the GRBs progenitors are massive stars. Moreover, it is also well accepted that the most massive stars (or at least a significant fraction of them) are members of binary system. This facts have motivated the theoretical approach to model the LGRBs, known as the...
In January 2020, the LIGO–Virgo detector network observed
gravitational-wave signals from two compact binary inspirals which are
consistent with neutron star–black hole (NSBH) binaries. These
represent the first confident observations to date of NSBH binaries
via any observational means. I discuss the characterstic of these
events and their level of confidence, what we can learn from them...
Understanding the nature of the stellar collapse plays an important role in a wide range of astrophysics. Stellar collapse produce the compact remnants (neutron stars and black holes) that make up a menagerie of exotic astrophysics objects from pulsars and X-ray binaries to the merging compact objects detected in gravitational waves. Stellar collapse plays an important role in most gamma-ray...
Numerical relativity simulations of compact-object binary coalescences have played an important role in the detection of gravitational wave observations and the characterization of the sources. As current detectors increase their sensitivity and future detectors join the effort, the role of numerical relativity will become more prevalent. I will provide an overview of the current status of...
Fast Radio Bursts (FRBs) are few-millisecond bursts of radio waves coming from far outside the Milky Way. Some repeat. Their origin is presently unknown as is whether they represent a single class of object or multiple classes. Recently there has been tremendous observational progress on understanding FRBs thanks to a variety of new instruments designed for their study. In this talk I review...
Fast radio bursts (FRBs) are cosmological millisecond-duration bursts in the radio band. The recent detection of the Galactic FRB 200428 suggests that magnetars can produce FRBs. In this talk, I will review the current understanding of the physical mechanisms of FRBs in reference of two related astrophysical phenomena, namely, radio pulsars and gamma-ray bursts. I will discuss the...
Our understanding of compact binary mergers was transformed by the spectacular discovery of GW170817, the first neutron star merger observed through gravitational waves and light. The electromagnetic counterpart of GW170817 was initially dominated by a luminous kilonova, peaking at optical and then infrared wavelengths. At 9 days, we detected in X-rays the onset of a different component of...
Insight-HXMT is China’s first X-ray astronomy satellite and was successfully launched on June 15th, 2017. It carries three sets of collimated X-ray instruments with large effective areas in 1-250 keV. In addition, it can also serve as a nearly all-sky monitor for high energy sources between 0.2 to 3 MeV, such as bright pulsars and gamma-ray bursts. I will review some highlights of the...
Time-domain astrophysics has been revolutionized by the advent of the multi-wavelength and multi-messenger era. The Einstein Probe (EP) is a space mission designed to discover and characterize high-energy transients and to monitor source variability in the X-ray band. Its large field-of-view telescope equipped with the micro-pore optic will carry out high-cadence all-sky monitoring survey with...
The X-Ray Imaging and Spectroscopy Mission (XRISM) is a JAXA/NASA X-ray observatory with collaboration from ESA and several institutes and academic institutions worldwide. It is proposed to fulfill the promise of high-resolution X-ray spectroscopy with imaging once realized but unexpectedly terminated by a mishap of ASTRO-H/Hitomi. XRISM carries two sets of X-ray Mirror Assemblies and is...
The Large High Altitude Air Shower Observatory is a new-generation multi-component instrument for TeV-PeV gamma rays and TeV-EeV cosmic rays. Recently, LHAASO has published its first result on the discovery of 12 ultrahigh-energy (E>100TeV) gamma-ray sources at more than 7 sigma confidence level. Among them, there are famous sources like the Crab Nebula, the Cygnus Cocoon, as well as new...
The eXTP (enhanced X-ray Timing and Polarimetry) mission is a major project of the Chinese Academy of Sciences (CAS), with a large involvement of Europe and expected ESA support. It is designed to study the state of matter under extreme conditions of density, gravity and magnetism, as for instance what is happening on the vicinity of black holes or what is the state of matter inside neutron...
I will present the SVOM mission that the Chinese National Space Agency and the French Space Agency havedecided to jointly implement for a launch in autumn 2022.In the line of Swift, SVOM has been designed to detect, characterize and quickly localize gamma-raybursts (GRBs) and other types of high-energy transients. For this task, the spacecraft will carry two widefieldhigh-energy instruments:...
The Southern Wide-field Gamma-ray Observatory (SWGO), is a new project for gamma-ray astrophysics in the energy range from a few hundred GeV up to a PeV. SWGO will be a steradian field of view, 100% duty-cycle detector, surveying the southern sky and monitoring for transient phenomena, as such it complements very well the planned flagship facility the Cherenkov Telescope Array. As the first...
Gamma Ray Bursts (GRBs) are bright backlights that can be used to probe the high redshift universe (z>6) when the first stars were born, galaxies formed and Hydrogen was reionized. Since the afterglow is bright only for a few days, speed is of the essence. Gamow Explorer is optimized to quickly identify high redshift events to trigger follow-up spectroscopic observations with JWST and >8m...
More than one hundred years ago, Albert Einstein published his Theory of General Relativity (GR). One year later, Karl Schwarzschild solved the GR equations for a non-rotating, spherical mass distribution; if this mass is sufficiently compact, even light cannot escape from within the so-called event horizon, and there is a mass singularity at the center. The theoretical concept of a 'black...
Increasing theoretical evidence supports the possibility that quantum theory replaces the black hole singularity with a quantum tunnelling to an anti-trapped region, and the blackhole horizon tunnels into a white hole horizon. I review the different elements supporting this intriguing scenario, and mention its possible astrophysical and cosmological implications.
We show that a magnetic charge in curved spacetime could be an artefact of a vacuum phase with zero metric determinant at a distance. This phase is characterized by a solution of the first-order field equations with nontrivial torsion. The monopole charge has a topological origin, given precisely by a lower-dimensional counterpart of the Nieh-Yan invariant in absence of matter. In this...
We introduce a novel model of affine gravity, which implements the no-scale scenario. Namely, in our model the Planck mass and Hubble constant emerge dynamically, through the mechanism of spontaneous breaking of scale invariance. This naturally gives rise to the inflation, thus introducing a new inflationary mechanism. Moreover, the time direction and non-degenerate metric emerge dynamically...
A large number of magnetized white dwarfs (WDs), with surface field strength generally less than 10$^9$ G, identified from wide-field surveys have helped us to understand their physical and chemical properties and the effect of magnetic field strength (B) on them. Though these weaker fields are not expected to modify their properties significantly, it is an excellent step for probing the...
In thus talk I will present the zoo of the High Mass X-ray Binary Systems (HMXBs). Among these I will discuss the X-ray/Be systems and in particular A0535 + 26/HDE245770. Through the multifrequency experimental data obtained in long observation campaigns it was possible to develop a particular model for the aforementioned system and then a general one that explains the delay between the flares...
The Generalized Chaplygin Gas (GCG) model is characterized by the equation of state P = −A ρ^{−α}, where A>0 and α < 1. The model has been extensively studied due to its interesting properties and applicability in several contexts, from late-time acceleration to primordial inflation. Nonetheless we show that the inflationary slow-roll regime cannot be satisfied by most of the parameter space...
The detection of gravitational waves from the binary neutron star merger, GW 170817, and subsequent short GRB as well as a kilonova signature and late afterglow confirmed a standing predictions and opened new fields of research. In this talk I will review early predictions, observations and interpretation as well as lessons that have been learnt. I will also review the exciting new line of...
Small scale CMB data contain a lot of cosmological information hidden in the different components : primordial CMB, tSZ effect, kSZ effect, CIB. Standard analyses assume templates for non primordial CMB components and lose the cosmological signature of large scale structures contained in secondary anisotropies. I will present a new analysis of SPT data at small scales where the tSZ spectrum is...
The nature of stellar progenitors and the associated explosion mechanism of type Ia supernovae (SNIa) remains one of the major open questions in astrophysics. Virtually all existing theoretical models require formation of a supersonic
detonation wave capable of providing nearly complete incineration of the
stellar material of a WD after it becomes gravitationally unbound. The
mechanism of...
