A Pulsar Timing Array (PTA) exploits the remarkable rotational stability of a sample of the rapidly spinning “recycled” pulsars in order to provide the possibility to search for gravitational waves (GWs) in the ultra-long period range, between few months to few decades. Therefore, by acting as galactic-scale GW detectors, the PTAs can explore a portion of the GW spectrum which is not charted...
Twistor theory was initially developed to describe the geometry of Minkowski space-time in terms of its null geodesics. The natural generalization to curved space-times requires the ubiquitous existence of α-surfaces, this requiring the Weyl curvature to be anti-self-dual, which for a real space-time implies conformal flatness. A bi-twistor, however, incorporates both a twistor and a...
In two recent papers submitted for publication to Phys. Rev. Letters on May 16, 2024 by R. Ruffini, C.L. Bianco, M. Prakapenia, H. Quevedo, J.A. Rueda, S.R. Zhang, the energy extraction process from the ergosphere of Kerr Black hole has been reconsidered, taking into account the effect of the Mirr. New concepts, as the energy extractable versus the extracted energy, are outlined. Pure...
Taiji is a Chinese space mission to detect gravitational waves with frequencies covering the range of 0.1mHz to 1.0Hz by utilizing a triangle of three spacecrafts in orbit around the Sun, which aims to probe the super (intermediate) mass black hole merges and extreme (intermediate) mass ratio in-spirals, to study the most challenging issues concerning the origin and evolution of massive black...
In this talk, we will explore the theoretical foundations of binary black holes and the revolutionary simulations in numerical relativity that have deepened our understanding of these objects. We will also showcase the remarkable achievements in observational astronomy made possible by gravitational wave observations, which have not only confirmed the existence of binary black holes but have...
Pulsar observations have been an important target for MeerKAT having two Large Survey Projects (MeerTIME and TRAPUM) dedicated to them. This has led to the discovery of more than 200 new pulsars within globular clusters, unidentified Fermi sources, the Magellanic clouds and the Galactic disk. These discoveries have pushed the boundaries of our knowledge of the pulsar properties. Furthermore,...
ChatGPT has been a highly discussed topic recently, capturing the attention of both professionals and the general public. It has sparked conversations about the impact of artificial intelligence (AI) on the world. As physicists and astrophysicists, we are interested in whether large language models (LLMs) can accurately analyze scientific data and produce valid physics results. In this...
Recent observations with the JWST and ALMA have identified at z > 10 massive star forming galaxies of up to 1011 solar masses that are already quench at z > 3. The very early formation and rapid evolution of massive galaxies produced great surprise, because it is difficult to reconcile with standard ΛCDM predictions. I will show that BH-jet feedback accelerated the formation and evolution of...
In this talk I will present a method devised to test the consistency between the background expansion and the evolution of cosmological perturbations. Such a test can be performed in a model independent way thanks to machine learning techniques and it will allow the detection of possible failures of the standard cosmological model, providing a direction to explore with alternative theoretical...
We reveal a new structure of black holes previously unexplored in the 20th Century. A black hole with an angular momentum and an angular velocity has a moment of inertia. It is a hidden property of the Kerr metric. When the rotation stops in an energy extraction process, there is an irreducible moment of inertia due to the irreducible mass of a Kerr black hole. The moment of inertia indicates...
Gamma-ray bursts (GRBs), as they are observed at high redshift (z = 9.4), are vital to cosmological studies and investigating Population III stars. To tackle these studies, we need correlations among relevant GRB variables with the requirement of small uncertainties on their variables. Thus, we must have good coverage of GRB light curves (LCs). However, gaps in the LC hinder the precise...
"Dark stars" are a theoretical class of celestial objects powered by dark matter annihilation rather than nuclear fusion. I will review the conditions in the early universe conducive to the formation of dark stars, covering the theoretical basis of dark matter annihilation as an energy source. I will discuss the expected properties of dark stars, including their size, luminosity, lifespan, and...
In this work, we investigate the impact of the Dark Energy Spectroscopic Instrument (DESI) 2024 data on dark energy scenarios. Specifically, we analyze three typologies of models, the first in which the cosmic speed up is related to thermodynamics, the second associated with Taylor expansions of the barotropic factor, whereas the third based on ad hoc dark energy parameterizations. In this...
Benetti M., Bentum M.-J., Bonetti L., Capozziello S., Dib A., Djeghloul N., dos Santos Filho L.R., Ellis J., Helayël-Neto J.A., Lämmerzahl C., López-Corredoira M., Mavromatos N.E., Perlick V., Randriamboarison O., Retinò A., Sakharov A.S., Sarkisyan-Grinbaum E.K.G., Sarracino G., Spallicci A.D.A.M., Vaivads A.
The ad-hoc dark Universe compatible to GR, faces the lack of experimental...
We review the contribution of undetected extragalactic sources to the cosmic microwave background (CMB) radiation, from radio to sub-millimetre wavelengths. As demostrated by very recent analyses, Active Galactic Nuclei (AGN) is the dominant population in this frequency
range, at least down to the $\simeq$ mJy flux density level in source number counts. As for this, number counts of...
The IceCube neutrino observatory recently found an excess of TeV neutrinos at a significance of 4.2 σ associated to NGC 1068, one of the most well known nearby Seyfert galaxies.
NGC 1068 was already known as a gamma-ray emitter in the GeV band, whereas only upper limits in the flux were found in the TeV band.
Interestingly, the neutrino flux is about two orders of magnitude larger than the...
The discovery of gravitational waves and their synergistic signatures
has opened immense opportunities for astrophysics. Significant
advancements in gravitational-wave detector technology, both on Earth
and in space, along with progress in electromagnetic and neutrino
observatories, have rapidly expanded our understanding of the cosmos. In
this talk, I will explore how this wholistic...
A well-known effect confirmed by astrophysical observations is the light deflection in the gravitational field. In the recent years, the Hamiltonian formalism has been frequently applied in analytical studies to discuss how a medium that surrounds the gravitating object changes the light bending compared to the absence of the medium. Within this formalism, the medium is usually regarded as a...
Even classical scalar fields, non-minimally coupled with the curvature, can violate energy conditions such as the null energy condition. In the context of quantum field theory, non-minimally coupled scalars can obey lower bounds, known as quantum energy inequalities, but these are always state dependent. In this talk I will discuss classical and quantum bounds on the null energy and consider...
We explore the properties of photospheric emission in gamma-ray bursts (GRBs) based on relativistic hydrodynamical simulations and Monte Carlo radiation transfer calculations. Our simulations confirm that photospheric emission gives rise to correlations between the spectral peak energy and luminosity that agree with the observed Yonetoku, Amati, and Golenetskii correlations. It is also shown...
Horizonless compact objects may produce phenomenological features which distinguish them observationally from black holes. In particular, the images of the accretion disks around them possess a characteristic morphology including a series of central bright rings instead of a black hole shadow. We demonstrate how the central ring structure arises relating it to the behavior of the deflection...
After more than two years of scanning the sky the eROSITA X-ray telescope aboard SRG orbital observatory produced the best ever X-ray maps of the sky and discovered more than three million X-ray sources, of which about 20% are stars with active coronas in the Milky Way, and most of the rest are galaxies with active nuclei, quasars and clusters of galaxies. eROSITA detected over 10^3 sources...
We demonstrate that the Raychaudhuri equation remains unchanged for certain solutions of scalar fields $\phi$ that have a non-canonical Lagrangian of the form $\mathcal{L}(X,\phi)=-V(\phi)F(X)$, with $X=\frac{1}{2} g_{\mu\nu} \nabla^{\mu}\phi \nabla^{\nu} \phi$ and $V(\phi)$ represents the potential. There are several solutions available for both homogeneous and inhomogeneous fields, which are...
Phenomenological studies in the last few years have provided significant support to the idea that the vacuum energy density (VED) is a running quantity with the cosmological evolution. Such a running actually helps in alleviating the cosmological tensions afflicting the ΛCDM. The theoretical studies backing up this approach go under the name of "running vacuum model" (RVM). Using this...
Selfdual gravity is a reformulation of general relativity on the phase space of an SL(2,C) gauge theory. As pointed out by Abhay Ashtekar in the mid 1980ies, this reformulation lead to a remarkable simplicity of Hamiltonian GR. Using selfdual variables, the constraints simplify and assume the simplest possible polynomial form. In this talk, I lay out a new non-perturbative lattice approach for...
I will review the properties and discuss some of the puzzling aspects of the unique binary system composed by the luminous hot subdwarf HD 49798 and a white dwarf of 1.220(8) solar masses and spin period of 13.2 s. This is one of the few massive white dwarfs with a dynamically measured mass and the one with the shortest spin period. It emits pulsed X-rays with a very soft spectrum, powered...
This work introduces the experimental progress of the measurement of gravitational constant G at Huazhong University of Science and Technology. We intend to carry out the measurement with the silicon spheres. The surface separation between the spheres is measured with the laser interferometry with an uncertainty of less than 0.1 um. The expected uncertainty of G is better than 10ppm.
The dense interiors of neutron stars provide a window to the nature of cold matter at densities above nuclear that complements precision laboratory nuclear experiments. The uncertain physics at high density leads to a range of possible equations of state (EOS). Since each potential EOS allows a different neutron star mass and radius curve, observations of many neutron star masses and radii...
We investigate the photon analogue of Fermi acceleration where a photon scatters within the shearing layers of a relativistic plasma and produces power-law-shaped spectra at high energies. It is an alternative to existing explanations of power law spectra such as synchrotron process or inverse Comptonization. Among several potential applications of this phenomenon, I will describe its...
The question of compatibility between our theory of gravity, more or less along the line of General Relativity, and basic notions of quantum physics has been a major concern. We focus, in particular, on an exact Weak Equivalence Principle and the notion of the momentum observable for a particle as a vector quantity with an invariant magnitude as given through the metric. Contrary to the...
In this talk I will firstly review the Schwinger effect in charged black holes and then introduce a remarkable alternative approach by using the monodromy. The explicit elaboration of monodromy and the model calculations seem to reveal evidences that the monodromy can provide a practical technique to study the spontaneous pair production in general black holes and electromagnetic fields.
The production mechanism of astrophysical high-energy neutrinos is not yet understood. A common assumption is that beamed relativistic outflows (jets) driven by accreting black holes are needed to accelerate particles to such high energies to produce high-energy neutrinos. Indeed, the first astrophysical high-energy neutrino source candidate identified by IceCube at a significance level of >3σ...
In this talk I consider the propagation of light rays, either in vacuum or in a non-magnetised pressure-less plasma, in axially symmetric and stationary spacetimes that describe wormholes. Among other things, I discuss the necessary and sufficient conditions for separability of the Hamilton-Jacobi equation (i.e., for the existence of a Carter constant) which allows complete integrability. For...
GRB spectra seem to be well fitted by models based on marginally fast-cooled synchrotron radiation. This observation challenges the synchrotron process as a viable mechanism as it leads to (too) large emission radii and (too) large bulk Lorentz factors. To overcome this difficulty, it was proposed that proton could be the particles radiating synchrotron emission. I will show that if protons...
The James Webb Space Telescope (JWST) is unveiling astounding results on the composition and evolution of the cosmo at very high redshifts. In this talk, I develop a UV luminosity function model for high-redshift galaxies, considering parameters such as the stellar formation rate, dust extinction, and halo mass function, calibrated at $z = 4\textrm{-}7$. Testing the model against higher...
The de Broglie-Proca theory, which endows the photon with a small, but finite rest mass, is the simplest extension of Maxwell’s electrodynamics. Over the last hundred years its consequences have been investigated both theoretically and experimentally with ever tighter upper bounds being set. In this talk we discuss recent limits/sensitivities on the photon mass from laboratory-based...
Compact objects are usually described using the perfect fluid formalism. However, in astrophysical processes out of local equilibrium, dissipative effects become important to realistically describe the dynamics of the system.
In this work, we present for the first time the gauge-invariant non-spherical perturbations in a dissipative self-gravitating fluid in spherical symmetry. For this we...
We examine the geometrical difference between non-extremal black hole(NXBH), extremal black hole(XBH) and naked singularity(NS) via Lense-Thirring(LT) effect in spinning modified-gravity(MOG). For NXBH, we find that the LT frequency ($\Omega_{LT}$) is proportional to the angular-momentum($J=a\,{\cal M}$) parameter or spin parameter($a$) i.e. $\Omega_{LT}\propto J $ or $\Omega_{LT}\propto a...
Novel proposal is made for candidate Fuzzy dark matter.Interestingly it has connections to primordial black holes which can seed supermassive black hole and play critical role in galaxy formation.
Gamma-ray bursts (GRBs) have been observed at very high redshifts, up to 9.4, and can be a crucial astrophysical object for studying the evolutionary history of the universe. However, the rapid dimming of their afterglows, combined with the constrained availability of telescope time, poses challenges in promptly observing these events. This difficulty is particularly pronounced for...
Astrometric data presented in ATNF Pulsar Catalogue have enabled us to determine the trajectories through the Galactic potential for different kick-velocity models of pulsars.
The system was disrupted ~0.2-0.8 Myr ago, which must correspond to the true age of at least one of the pulsars. The implied pulsar birth velocities are consistent with the high velocities of neutron stars in general....
The Preferred Frame Effects (PFE), in the framework of the Parametrized-Post Newtonian (PPN) formalism, valid in the weak-field and slow-motion (WFSM) limit of General Relativity (GR), are described by the three parameters α1, α2 and α3, all equal to zero in GR and in tensor-scalar theories of gravity. A test of PFE is equivalent to a test of Local Lorentz Invariance (LLI), which represents a...
About a billion years after the Big Bang, the Epoch of Reionisation saw the first light sources in the Universe slowly ionise the primordial atoms of the surrounding IGM. Learning about this distant epoch has the potential of unveiling crucial information about the formation of the first stars, galaxies, and early black holes, which sourced it.
One particularly promising probe of this epoch...
The persistence in some of the tensions and anomalies that affect the standard model of cosmology, like the $H_0$-tension, the $\sigma_8$-tension and the lensing anomaly, has motivated the study of alternative models capable of dealing with them. We re-analyze some of the most common extensions of the $\Lambda$CDM model in addition to other more theoretically motivated models in light of...
We discuss the entanglement entropy for a massive Klein-Gordon field in two Schwarzschild-like quantum black hole spacetimes, also including a nonminimal coupling term with the background scalar curvature. To compute the entanglement entropy, we start from the standard spherical shell discretisation procedure, tracing over the degrees of freedom residing inside an imaginary surface. We...
The adiabatic regularization method is likely the most direct and intuitive subtraction scheme for FLRW cosmologies. The method requires one to start with a nonvanishing mass, but massless theories can be studied by taking the massless limit at the end of the calculations. In fact, the conformal anomaly for scalar fields was first derived with the adiabatic method by taking the massless limit....
We construct boson star configurations in quantum field theory using the semiclassical gravity approximation. Restricting our attention to the static case, we show that the semiclassical Einstein-Klein- Gordon system for a single real quantum scalar field whose state describes the excitation of N identical particles, each one corresponding to a given energy level, can be reduced to the...
An overview of highlights and discoveries from Mikhail Pavlinsky ART-XC telescope on board the SRG observatory is presented. Since 2019 SRG/ART-XC has conducted several full all sky surveys as well as a deep survey of our Galaxy. As a result, we obtained the catalogue of hard X-ray sources detected at the all sky, which includes more than one and a half thousand objects, most of them are...
Type-I X-ray bursts are powered by the unstable thermonuclear burning of accreted hydrogen and helium material on the surface of a neutron star (NS) in low-mass X-ray binary systems. They typically last for tens to hundreds of seconds, depending on the fuel composition. Among the observed bursts, approximately 20% of them are powerful enough to lift the NS photosphere tens to hundreds of...
In this talk, I will present two recent models for explaining the observed GRB spectra.
As a GRB jet drills its way through the collapsing star, it traps a baryonic "cork" ahead of it. If the jet does not cross this cork, but rather photons that are emitted deep in the flow (e.g., by pair annihilation) are scattered by the cork, an observer close to the jet axis will see these photons due to...
In loop quantum gravity (LQG), the volume operator plays a crucial role in the study of quantum geometry and quantum dynamics. However, the effect of the volume operator is studied only for some simple cases. In this talk, we introduce a numerical algorithm that can give the matrix elements of the volume operator on arbitrary valent gauge-variant and gauge-invariant spin network states and...
I discuss sensitivity of black hole thermodynamics to certain boundary terms in the action. While boundary terms cannot affect the classical gravitational dynamics, they apparently influence both the black hole entropy and temperature. Remarkably, this behaviour is confirmed by two standard approaches to black hole thermodynamics; the covariant phase space (Iyer-Wald) and the Euclidean...
With the proliferation new and more sensitive detector technologies, coincident observation of triggers for two or more messengers (gravitational-waves, electromagnetic, neutrinos) will become increasingly frequent. I will discuss implications and unmet needs for the observational-data rich future when low-latency subthreshold triggers will be publicly available for several messenger types and...
Current images of the supermassive black hole (SMBH) candidates observed at the center of our Galaxy and M87, have opened an unprecedented era to study both, gravity in its strong regime and the very nature of the relativistic sources. Very-long-baseline interferometry (VLBI) data show images consistent with a central black hole as predicted by General Relativity (GR). However, it is important...
Over more than a decade, along with my group members I have been
exploring the possible violation of Chandrasekhar mass-limit significantly
and possible new mass-limit(s). They are indirectly supported by some
observations of peculiar type Ia supernovae. The potential reasons behind
such a violation could be magnetic field, modified gravity, noncommutative
spacetime etc. Many other groups...
We reflect on the possibility of breaking the diffeomorphism (Diff) invariance in the gravitational couplings of matter down to only transverse diffeomorphisms (TDiff), and study the consequences on a scalar field theory. We then explore the possibility of restoring the full Diff invariance preserving the locality of the theory by the introduction of an additional vector field. From the...
The Transitional Planck Mass (TPM) model is a useful application of the Effective Field Theory of Dark Energy and Modified Gravity, characterized by a step-like transition in the Planck Mass at cosmological scales. This transition, occurring during the radiation era, has shown efficacy in mitigating the Hubble tension. It achieves this by decreasing the sound horizon as detected by Cosmic...
We show that because in a curved spacetime parallel transportations of (r,s)- tensors with r+s>0
depend on paths, one cannot add up (r,s)-tensors at different points to get a definite sum
(r,s)-tensor when r+s>0. However, when restricted to an infinitesimal spacetime region, one still
can add up (r,s)-tensors at different points to get a definite sum (r,s)-tensors, if neglecting
higher...
Two lessons learned from Planck was the importance of global analysis of instrumental, astrophysical and cosmological parameters as well as the usefulness of joint analysis of multiple datasets for component separation purposes. These lessons has been further developed into a coherent pipeline for global analysis of multiple datasets by BeyondPlanck and Cosmoglobe, which has been successfully...
Large-scale cosmic emissions of explosive energy that occur during the explosions of certain supernovae or the merger of compact objects are called gamma-ray bursts. We study the radiation of the ultrarelativistic shell in the diffusion approximation, which takes place at the initial stage of a gamma-ray burst. We get the effective temperature, instantaneous and time-integrated spectra for the...
I will discuss eternal inflation and the key role that inflation plays in resolving cosmological singularities. I will describe how proposed no-go theorems, such as the famous theorem of Borde, Guth and Vilenkin (BGV) are circumvented or obviated. Our exploration encompasses eternal inflating, loitering, and bouncing models, shedding light on the critical aspects that underpin geodesic...
Similar to Dirac models of nanostructures, low-energy excitations in spin systems --magnons-- can be described in terms of effective field theories. The theory describing antiferromagnets can be mapped into scalar massless electrodynamics with an external electromagnetic potential. Here, we consider the case of a constant inhomogeneous magnetic field applied to an antiferromagnet, whose...
We consider repetitive decays in the ergosphere of an initially extreme Kerr BH and show that these processes are highly irreversible. For each decay, including the BH capture of the particle falling into the horizon, the increase of the irreducible mass is much larger than the extracted energy. By considering the decay at different points within the ergosphere, we conclude that the repetitive...
The Newtonian law of non-relativistic gravity has been tested in many laboratory experiments with very high precision. In contrast, the gravitational field of ultra-relativistic matter, dominated by kinetic energy and stresses, has not been measured directly. I will examine the gravitational field of moving source masses in general relativity and scalar-tensor theory. The latter serves as an...
The X-ray afterglow of many gamma-ray bursts (GRBs) exhibits a plateau phase, which may be related to continued activities of the central engine. It has been found that there exists a so-called L–T–E correlation for these GRBs, which involves three key parameters, i.e., the isotropic gamma-ray energy Eiso of the prompt phase, the end time Ta of the plateau phase, and the corresponding X-ray...
The standard interpretation of the redshifts of galaxies is that they are due to the expansion of the universe plus peculiar motions, but there are other explanations, such as the "tired light" hypothesis, which assumes that the photon loses energy owing to some unknown photon-matter process or photon-photon interaction when it travels some distance. Different observational tests give...
Early James Webb Space Telescope (JWST) observations defied expectations from the standard 𝚲CDM model of cosmology. There is an overabundance of very massive, high-redshift galaxies and quasars when the universe was only a few hundred million years old. Supermassive Dark Stars (SMDS) offer a potential solution to this paradox. They are candidates for the first stars in the universe, alongside...
In this talk we show that the relevant physical information in the construction of a vacuum state is encoded in the selection of a Lagrangian subspace of the space of complexified solutions. In particular we show the existence of a one-to-one correspondence between vacuum states for qft in curved spacetime and Lagrangian subspace. This result implies a unification of a general notion of...
Pulsars are promising sources of gravitational waves (GWs). While asymmetric mass distributions will produce continuos GWs, sudden relocations of small fractions of the internal neutron superfluid could produce transient GW emission. Such rearrangements are believed to be responsible for rapid accelerations in rotation, known as glitches, which have been observed in hundreds of pulsars. The...
We estimate the neutrino flux from different kinds of galactic sources and compare it with the recently diffuse neutrino flux detected by IceCube. We find that the flux from these sources may contribute to ∼20% of the IceCube neutrino flux. Most of the sources selected in this work populate the southern hemisphere, therefore a detector like KM3NeT could help in resolving the sources out of the...
We explore in detail the time-dependent simulation for the evolution of the magnetized main sequence (MS) stars to magnetised white dwarfs (WDs) using the Cambridge Stellar evolution code: STARS. In order to do so, we have appropriately modified the said code by introducing magnetic effect and cooling. We investigate further the possible existence of stable, massive, super-Chandrasekhar WDs,...
Many notions of entropy have been formulated in Physics, from thermodynamics to statistical mechanics and information theory. Bekenstein and Hawking, relying on completely different physical arguments than each other's, pioneered the idea of gravitational entropy claiming that the gravitational field of an empty space
black hole as Schwarzschild comes with an entropy equal to one fourth of...
We explore a model in modified $f(R)$ gravity where the modification in geometrical part of the Einstein-Hilbert action leads to complete elimination of the need for dark matter and dark energy, both. This is specifially obtained by the scalar fields induced in the Einstein's gravity whose dynamical oscillations account for the effects (otherwise attributed to dark matter and dark...
One of the main arguments in favour of magnetically dominated outflows is the absence of photospheric component in their broad-band time-resolved spectra, with such notable example as GRB 080916C. Detection of subdominant thermal component in this GRB is actually consistent with the photosphere of ultrarelativistic baryonic outflow, deep in the coasting regime. Therefore, the magnetic...
We will present a mathematical formulation of Ashtekar variables using the language of differential topology, aligning as closely as possible with the mathematical description of Yang-Mills theories. This approach illuminates the similarities while highlighting the differences between the two.
Additionally, within this framework, we can properly discuss the imposition of symmetries at the...
There are observations supporting the plausible modification to Einstein
gravity, while the exact theory of gravity in the strong field regime is
indeed under debate. We obtain a new black hole solution in an f(R)-gravity-based
modified gravity. Such a black hole evaporates faster by Hawking radiation
compared to that in the Einstein gravity, i.e. the Kerr black hole.
One of its...
Conformal Field Theory in momentum space allows to investigate effective actions related to the Trace Anomaly of the Stress energy Tensor in great detail. The resulting action is nonlocal and can be investigated in general metric backgrounds. The method of reconstruction of the action is worked out, in our analysis, both around flat spacetime and for general backgrounds, by comparing the...
The cosmic infrared background (CIB) is sourced by the dusty star-forming galaxies throughout the Universe and spans a wide range of redshifts. Its measurements are thus a powerful tool to map the star formation at high redshifts and understand the connection between the host dark matter halos with the galaxies residing in them. Also, in synergy with the cosmic microwave background (CMB), the...
We present the strategy, analysis, and results of our four-year timing program of RX J0806.4-4123 with NICER. RX J0806.4-4123 belongs to the group of radio-quiet X-ray thermal isolated neutron stars (XTINSs) that are located between the rotation-powered pulsars and the magnetars in the P-Pdot diagram. The slowly rotating XTINSs constitute a key population to learn about the structure, physics...
In this research, we examine the gravitational behavior of dense astronomical bodies, specifically white dwarfs and neutron stars, using Einstein's gravitational theories. We explore the effects of deviations from spherical symmetry by applying a simplified mathematical model, incorporating the quadrupole moment to a first-order approximation [1].
Focusing on the interiors of white dwarfs, we...
Electromagnetism is one of the pillars of modern physics and until very recently was nature’s sole
messenger. The avenue of multi-messenger astronomy in the recent year is opening a whole
new world of observations and promises great advances for science, but nonetheless still relies
on electromagnetic waves as a core component.
Extended theories of electromagnetism impact thus directly our...
Gamma-ray bursts (GRBs) can be probes of the early universe, but currently, only 26% of GRBs observed by the Neil Gehrels Swift Observatory GRBs have known redshifts (z) due to observational limitations. To address this, we estimated the GRB redshift (distance) via a supervised statistical learning model that uses optical afterglow observed by Swift and ground-based telescopes. The inferred...
In hierarchical triple systems, the inner binary can be considered as a rotating matter ring with respect to the distant, outer companion. As such, the orbital angular momentum of the former induces an own gravitomagnetic field which may be orders of magnitude larger than that due to the individual spin angular momenta of the binary's components.The resulting gravitomagnetic orbital...
That light propagating in a gravitational field gets
frequency-shifted is one of the basic consequences of any metric theory
of gravity rooted in the equivalence principle. At the same time, also a
time dependent material's refractive index can frequency-shift light
propagating in it. The mathematical analogy between the two effects is
such that the latter has been used to study the...
JWST’s discoveries of black holes with masses ∼ 108M⊙ when the Universe was less than 5% of its current age challenge our understanding of star and black hole formation. The leading hypothesis to explain these observations is the inflowing of a large amount of gas directly onto the SMBH from galaxy-wide scales while maintaining gas stability against star formation. However, alternatives in...
The dynamical stability of differentially rotating neutron stars
is of paramount importance in understanding the fate of the post-merger remnant of binary neutron stars mergers and the formation of black holes during core collapse supernovae. We study systematically
the dynamical stability of differentially rotating neutron stars for a broad range of masses, rotation rates and degrees of...
AstroSat is a multiwavelength astronomy satellite with a suite of instruments facilitating simultaneous observations of cosmic objects in the optical, ultraviolet, soft X-ray, and hard X-ray ranges. The capabilities of these science payloads include a large collection area, high time resolution, excellent imaging, and hard X-ray polarization. AstroSat has observed varieties of cosmic...
Reconstructing the expansion history of the universe and properties of dark energy have been among the main goals of physical cosmology. I will discuss about reconstructing dark energy in light of most recent cosmological observations including DESI-2024 BAO observations, Union3 supernova compilation and Planck CMB data.
Shibata and Sasaki [Phys. Rev. D 60, 084002 (1999)] introduced the so-called compaction function. Since then, it has been empirically established that the maximum value of this function (or its volume-averaged counterpart) in the long-wavelength solutions gives a very robust threshold of primordial black hole formation. In this paper, we show that in spite of initial intention, the...
Higher-order photon rings can be expected to be detected in a more detailed image of the black hole found in future observations. These rings are lensed images of the luminous matter surrounding the black hole and are formed by photons that loop around it. We have succeeded to derive an analytical expression for the shape of the higher-order rings in the form that is most convenient for...
We discuss general solutions of the Einstein-Cartan theory sourced by a cosmological perfect fluid composed of particles with intrinsic spin. In the considered model, the metric tensor is described by a general FLRW solution, however, the Weyl tensor might not vanish. The coupling between the intrinsic spin and the Weyl tensor excludes spatially closed solutions, and the universe must either...
Over the last decade, the scenario of choked jets embedded in core-collapse supernovae (CCSNe) has attracted careful attention. The extended stellar envelopes of red supergiant (RSG) and blue supergiant (BSG) stars, both progenitors of Type II SNe, may constitute a challenge to the launch of a powerful jet able to burrow through their envelopes. As the jet carves its way through them, it...
Gamma-ray bursts (GRBs) are the brightest sources in the Universe.
They appear as gamma-ray flashes, with a spectrum that peaks around a few hundred keV . The prompt spectra of GRBs were historically characterised through the phenomenological Band function, composed of two power laws smoothly connected around the peak. Because of the broad spectral shape, GRB spectra seem consistent with...
Black holes are among the most challenging objects to study in the universe since nothing can escape from their event horizon. Fortunately, these objects leave traces by imposing their extreme gravitational pull on the surrounding matter as it falls into the black hole. Spectral-timing analysis has become very popular for studying accreting black holes and inferring the geometrical structure...
Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. How efficiently the jet converts its energy to radiation is a long-standing problem and it is poorly constrained. The standard model invokes a relativistic fireball with a bright photosphere emission component. A definitive diagnosis of GRB radiation components and measurement of GRB radiative efficiency require prompt...
The division of gamma-ray bursts (GRBs) into different classes, other than the ‘short’ and ‘long’, has been an active field of research. We investigate whether GRBs can be classified based on a broader set of parameters, including prompt and plateau emission ones. Observational evidence suggests the existence of more GRB subclasses, but results so far are either conflicting or not...
We here explore a specific class of scalar field, dubbed quasi-quintessence which exhibits characteristics akin to ordinary matter. Specifically, we investigate under which conditions this fluid can mitigate the classical cosmological constant problem. We remark that, assuming a phase transition, it is possible to predict inflationary dynamics within the metastable phase triggered by the...
We construct a (quantum mechanically) modified model for the Oppenheimer-Snyder collapse scenario where the exterior of the collapsing dust ball is a Hayward black hole spacetime and the interior is a dust Friedmann-Robertson-Walker cosmology. This interior cosmology is entirely determined by the junction conditions with the exterior black hole. It turns out to be non-singular, displaying a...
When charged fermions gyrate within a uniform magnetic field, their energy undergoes quantization into discrete levels known as Landau levels, a phenomenon termed Landau quantization. This effect finds diverse applications, ranging from the quantum Hall effect and the de Haas Van Alphen effect to the formation of super-Chandrasekhar white dwarfs. In a uniform magnetic field, Landau levels...
On June 9th, we received the news of the passing of Professor Manuel Malheiro. Malheiro was not only a colleague and advisor, but also a friend. This presentation covers our last work together and represents my homage to him.
The lack of isolated neutron stars~(NSs) rotating slower than 11 s led to the postulate of a maximum limit for their rotation period. However, the discovery of radio...
We study static and spherically symmetric black hole (BH) solutions in extended Einstein- Maxwell-scalar theories which is classified in a subclass of the $U(1)$ gauge-invariant scalar-vector- tensor theories. The scalar field is coupled to the vector field, which has electric and magnetic charges. We investigate modifications to the Reissner-Nordstr ̈om solution focusing on the three types of...
Gravitational lensing of luminous matter that surrounds a black hole or some other sufficiently compact object produces an infinite sequence of images. Besides the direct (or primary) image, it comprises demagnified and deformed replicas of the original known as photon rings which are progressively nearing the boundary of the socalled shadow.
We present analytical approximation formulas for...
Abstract: Stueckelberg solved the problem of gauge invariance
in massive
QED by a new mechanism which is precursor for Abelian Higgs.
It has several implications in Cosmology and we will discuss few of
them.
Many stripped-envelope supernovae (SNe) present a signature of high-velocity material responsible for broad absorption lines in the observed spectrum. These include SNe associated with long gamma-ray bursts (LGRBs), low-luminosity GRBs (llGRBs), and SNe not associated with GRBs. It was recently suggested that this high-velocity material originates from a cocoon driven by a relativistic jet. In...
If two particles move towards a black hole and collide in the vicinity of the horizon, under certain conditions their energy Ec.m. in the center of mass frame can grow unbounded. This is the Banados-Silk-West (BSW) effect. Usually, this effect is considered for extremal horizons and geodesic (or electrogedesic) trajectories. We study this effect in a more general context, when both geometric...
The chameleon-induced polarization modes of gravitational waves (GWs) are explored in f(R) gravity arising due to scalar field. The chameleon mechanism works strongly in high density regions where mass of the scalar field particle becomes high and the oscillations of the scalar field sharply increase. This produces enhanced scalar modes in addition to the tensor modes of polarization in...
In this talk, I will present and discuss evidence for cocoon emission in the early afterglow emission phases of the nearby GRB-SN 171205A. Special attention will be given to the multi-wavelength analysis, and to modeling of the cocoon component.
The peculiar motion of an observer relative to an ideal reference frame at rest with respect to the cosmic background produces boosting effects which modify and transfer at higher multipoles the frequency spectrum of the isotropic background. To mitigate the computational effort needed for accurate theoretical predictions, I present analytical solutions of a linear system able to evaluate the...
In this talk I will first review the late-time phenomenology required to solve the Hubble tension, making especial emphasis on the pivotal role played by the data on baryon acoustic oscillations (BAO) in the building of the inverse distance ladder. I will show, in particular, how the angular (2D) and anisotropic (3D) BAO data, despite being obtained from the same parent catalogues of tracers,...
The light curves (LCs) of long gamma-ray bursts (GRBs) show a wide variety of morphologies, which current LC simulation models based on the internal shock paradigm still fail to fully reproduce. The reason is that, despite the recent significant advance in understanding the energetics and dynamics of long GRBs, the nature of their inner engine, how the relativist outflow is powered, and the...
We present a systematic approach to the kinematics of quantum-reduced loop gravity, a model originally proposed by Alesci and Cianfrani as an attempt to probe the physical implications of loop quantum gravity. In order to implement the quantum gauge-fixing procedure underlying quantum-reduced loop gravity, we introduce a master constraint operator on the kinematical Hilbert space of loop...
Nano-electromechanical systems (NEMS), electrostatically driven at their resonance frequency and parametrically pumped by time-dependent dispersion forces, are theoretically expected to display remarkable gain, sensitivity, resolution, and tunability properties. This author previously discussed employing nanodevices of this novel class as sensors to measure non-gravitational accelerations in...
The origin of supermassive black holes (SMBHs) is a key open question for contemporary astrophysics and cosmology. Here we discuss the predictions of a model of SMBH formation from Pop III.1 protostars, i.e., metal-free stars forming in locally isolated dark matter minihalos, where dark matter annihilation has a chance to alter the structure of the star allowing growth to supermassive scales...
The Galactic X-ray black hole candidate GRS 1915+105 exhibits high-frequency quasi-periodic oscillations (HFQPOs) at ~ 67 Hz only during the radio-quiet 'softer' variability classes. We have studied the long-term X-ray variability from 1996 to 2017 using observations from RXTE, AstroSat, NuSTAR and NICER. AstroSat observations reveal the first detection of a soft-lag for higher energy photons...
Particle detector models have been recently proven to be an effective mean to know how curved spacetimes affect quantum systems. For example, particles generated by the Unruh effect could be detected by an accelerating system and can provide a reliable communication of quantum messages, usually prevented by the no-cloning theorem. Motivated by this fact, we propose a quantum communication...
We show by matching two flat spaces one in Minkowski coordinates ( empty space) and the other in Minkowski coordinates after a special conformal transformation (also empty space) through a bubble with positive and constant surface tension, that the motion of the bubble is hyperbolic. If the surface tension is very big the initial size of the bubble is as small as we wish, so that we can indeed...
The gravitational memory effect and its electromagnetic (EM) analog are potential probes in the strong gravity regime. In the literature, this effect is derived for static observers at asymptotic infinity. While this is a physically consistent approach, it restricts the spacetime geometries for which one can obtain the EM memory effect. To circumvent this, we evaluate the EM memory effect for...
We explore the stability of this rapidly rotating WD using a modern equation of state (EoS) that accounts for electron–ion, electron–electron, and ion–ion interactions. For this EoS, we determine the mass density thresholds for the onset of pycnonuclear fusion reactions and study the impact of microscopic stability and rapid rotation on the structure and stability of WDs, considering them with...
The trace anomaly is the breaking of Weyl ($\sim$ scale) invariance upon quantisation of a theory, and occurs in a gauge and/or gravitational background. The presence of the parity violating Pontryagin densities $R\tilde R$ and $F\tilde F$ in the trace anomaly could have far reaching phenomonological consequences, and have been the subject of debates over the past decade.
In our latest work...
All particles created through the Hawking process have to be generated in the collapsing object. The black hole internal states should be related to the precollapsed state (a one-to-one correspondence between the internal state and precollapse configuration).
The baryons that formed the initial collapsing star cannot reappear since all their rest energy has been carried away by the thermal...
AGILE is a high-energy astrophysics space mission launched in 2007 which terminated the operations in 2024. Its payload is comprised of the Gamma-Ray Imaging Detector (GRID), the SuperAGILE X-ray detector, the Mini-Calorimeter (MCAL), and an AntiCoincidence System (ACS).
Over the past few years, the AGILE Team has developed deep learning (DL) models to analyze sky maps and time series...
Supermassive black hole binaries (SMBHBs) represent the latest stage in the hierarchical growth of massive galaxies through major mergers. In these systems, accretion onto the black holes is expected to form two individual accretion disks around each black hole, fed by a larger circumbinary disk. Consequently, the X-ray and UV emission from these systems is expected to vary regularly, with...
GRB afterglows are powered by emission from relativistic collisionless shocks.
The converter acceleration mechanism, which is specific just for
relativistic shocks, makes them efficient emitters and at the same time
modifies the shock structure. As a result, the shock balances itself within
a region in the parameter space that can be estimated analytically or
evaluated numerically with...
The Kerr spacetime is one of the most relevant spacetimes in contemporary astrophysics and describes the spacetime of a rotating black hole. When light rays pass by or are emitted in the close vicinity of a Kerr black hole they are gravitationally lensed and this leads to characteristic lensing features on the sky of a distant observer. While it is a common assumption that the observer is...
Supernova (SN) 2023ixf in M101 is the closest SN explosion observed in the last decade. Therefore, it is a suitable test bed to study the role of jets in powering the SN ejecta. With this aim, we explored the idea that high-energy neutrinos could be produced during the interaction between the jets and the intense radiation field produced in the SN explosion and eventually be observed by the...
Based on the Poincare gauge theory of gravity with the most general Lagrangian quadratic in curvature and torsion, we investigate the axial vector torsion-spin coupling. The dynamical equations for the so-called “electric” ${\mathcal E}_a $ and “magnetic” ${\mathcal B}^a$ components of the torsion variable are obtained in the general form, where the helicity density and spin density of the...
This study focuses on constructing physical model of spherically
symmetric systems incorporating electromagnetic fields within the
framework of f (Q) gravity. To achieve this, we derive the field equations corresponding to f (Q) gravity in the presence of anisotropic matter, and then connect the interior space-time with the exterior Reissner
Nordstrom metric to determine the constants...
Given a base manifold $M$ and a Lie group $G$, we define $\widetilde{\cal A}_M$ a space of generalized $G$-connections on $M$ with the following properties:
- The space of smooth connections ${\cal A}^\infty_M = \sqcup_\pi {\cal A}^\infty_\pi$ is densely embedded in $\widetilde{\cal A}_M = \sqcup_\pi \widetilde{\cal A}^\infty_\pi$; moreover, in contrast with the usual space of generalized...
Supermassive dark stars (SMDS) are luminous stellar objects formed in the early Universe at redshift $z \sim 10-20$, made primarily of hydrogen and helium, yet powered by dark matter.
We examine the capabilities of the Roman Space Telescope (RST), and find it able to identify $ \sim 10^6M_{\odot}$ SMDSs at redshifts up to $z\sim 14$. With a gravitational lensing factor of $\mu\sim 100$, RST...
The origin of the prompt emission in gamma-ray bursts (GRBs) remains debated. Our understanding is primarily derived from wide-field telescopes that operate within the 10 keV-10 MeV range. However, capturing early emissions at higher energies (above 100 GeV) is challenging because of the time required for slewing of the telescopes. I will discuss multi-messenger observational strategies aimed...
Cosmological inflation is a popular paradigm for understanding Cosmic Microwave Background Radiation (CMBR); however, it faces many conceptual challenges. An alternative mechanism to inflation for generating an almost scale-invariant spectrum of perturbations is a bouncing cosmology with an initial matter-dominated contraction phase, during which the modes corresponding to currently observed...
Our idea is to state that a particular set of values and reformulation of initial conditions for relic black holes, as stated in this manuscript , will enable using the idea of Torsion to formulate a cosmological constant and resultant Dark Energy. Relic Planck sized black holes will allow for a spin density term which presents an opportunity to modify a brilliant argument given as to...
There are several quantum phenomena that can be described in a semiclassical approach, such as the Hawking effect, Schwinger pair production and the Casimir effect.
In this talk we will focus on the role of resummations in this framework, which are necessary if one wants to access the nonperturbative regime. We will give a general overview of results valid for quantum fields in curved...
Double white-dwarf (DWD) mergers are relevant astrophysical sources expected to produce massive, highly-magnetized WDs, supernovae (SNe) Ia, and neutron stars (NSs). There are expected to be numerous sources in the sky, but none have been yet detected, evading the most advanced transient surveys (e.g., The Zwicky Transient Facility - ZTF). We characterize the optical transient from DWD...
Solutions of the usual wave equation involve two arbitrary constants since it is a
linear second order ordinary differential equation. Physically, these constants represent the amplitude and frequency of the waves. It is not a priori clear that “nonlinear wave equations” must possess two constants as well. However, the exact solutions of the nonlinear Einstein Field Equations for plane and...
Functional flow equations based on proper-time (PT) regulators have attracted much interest in recent years because of their effectiveness in various non-perturbative situations, for example the exploration of the ordered phase in a scalar theory or non-perturbarive quantum gravity. In this talk in particular we study the flow of the non-local truncation in quantum gravity and we focus in...
Gamma-ray bursts (GRBs) exhibit a diversity of spectra. Several spectral models (e.g., Band, cutoff power-law, and blackbody) and their hybrid versions (e.g., Band+blackbody) have been widely used to fit the observed GRB spectra. Here, we attempt to collect all the bursts detected by {\it Fermi}-GBM with known redshifts from July 2008 to May 2022, motivated to (i) provide a parameter catalog...
Thanks to its all-sky coverage, the Planck mission had the unique capability of detecting the brightest strongly lensed high-z galaxies in the sky. The combination of boosted luminosity and stretching of images offers a unique opportunity to pierce into their internal structure and dynamics via high-resolution follow-up observations. It becomes possible to reach spatial resolutions of tens of...
The possibility that the vacuum energy density (VED) could be time dependent in the expanding Universe is intuitively more reasonable than just a rigid cosmological constant for the entire cosmic history. The framework of the running vacuum model (RVM) is a remarcable example, in which the VED appears as a power series of the Hubble rate, H(t), and its derivatives. The RVM contributes to...
The last century has seen tremendous improvements in our understanding of electromagnetism. An important discovery was made by Einstein in 1916, who combined thermodynamics and atomic physics to predict stimulated emission. The quantization of Maxwell's Equations yielded a powerful tool, Quantum Electrodynamics, which produced extremely accurate predictions as well as explained a large...
Astronomy has entered a new era of multi-messenger observation with the early detection of neutrinos from SN1987A and the recent discovery of gravitational waves. Neutrinos serve as an effective detection channel for various astrophysical sources. This research focused on neutrino propagation through multiple media, including central engines within gamma-ray bursts (GRBs) and environments...
A new subclass of transients spatially coincident with centers of galaxies have been uncovered in the past few years. One of the leading hypothesis for these repeaters is that they could be driven by objects orbiting massive black holes. I will give an overview of how NICER's large effective area and excellent maneuverability have been instrumental in making these discoveries.
We propose a model-independent Bézier parametric interpolation to alleviate the degeneracy between baryonic and dark matter abundances by means of intermediate-redshift data. To do so, we first interpolate the observational Hubble data to extract cosmic bounds over the (reduced) Hubble constant, h0, and interpolate the angular diameter distances, D(z), of the galaxy clusters, inferred from the...
The second brightest GRB in history, GRB230307A provides an ideal laboratory to study the details of GRB prompt emission thanks to its extraordinarily high photon statistics and its single broad pulse overall shape characterized by an energy-dependent fast-rise-exponential-decay (FRED) profile. Here we demonstrate that its broad pulse is composed of many rapidly variable short pulses, rather...
The aim of this study is to explore some features of the nonperturbative, one-loop, regularized effective Lagrangian of scalar quantum electrodynamics (QED) in a uniform electric field background with constant energy density in the Poincare patch of 2-dimensional de Sitter spacetime ($\mathrm{dS}_{2}$). Particularly, the electric permittivity of the vacuum, and the equation of state of the...
We present an approach to field quantization in curved spacetime which is based on the De Donder-Weyl Hamiltonian theory where space and time dimensions are treated on an equal footing. This leads to a description in terms of Clifford algebra valued wave functions on the bundle of field variables an spacetime variables, and a Dirac-like analog of the Schroedinger equation for this universal...
Singularities in Newton's gravity, in general relativity (GR), in Coulomb's law, and elsewhere in classical physics, stem from two ill conceived assumptions that, a) there are point-like entities with finite masses, charges, etc., packed in zero volumes, and b) the non-quantum assumption that these point-like entities can be assigned precise coordinates and momenta. In the case of GR, we...
In 1929, Carnegie astronomer Edwin Hubble discovered that the universe is expanding, and revolutionized our perspective on the universe. Decades of discovery followed. The launch of the Hubble Space Telescope (HST) in 1990 enabled astronomers to make measurements of the universe of unprecedented accuracy. Professor Freedman will describe how astronomers measure how fast the universe is...
This year marks the anniversary of the discovery of the Hulse-Taylor pulsar, which ushered in a a new era in the study of relativistic gravity. This Nobel Prize-winning discovery not only provided evidence for the existence of gravitational waves, but also led to the development of new methods and new studies of phenomena under strong field conditions. These included effects such as light...
In this talk will first review some highlights of the scientific results of Insight-HXMT,China’s first X-ray astronomy satellite launched on June 15th, 2017. I will then introduce the future mission eXTP (enhanced X-ray Timing and Polarimetry), planned for launch around 2028, to explore the physics under the extreme conditions of gravity, magnetism and density by making precise observations of...
General Relativity and quantum mechanics are both universally applicable theories and are most important for our present understanding of matter, space and time. Clearly, both theories have to be tested as good as possible. In this talk an overview is given of recent tests of both theories like the Equivalence Principle, equivalence of active and passive gravitational mass, the redshift, the...
A brief reminder of the case for particle dark matter and general search strategies will be followed by a description of the XENON dark matter program. The main part of the talk will cover details about the currently running XENONnT detector, the latest results and an outlook on future plans.
One of the most powerful tests of our cosmological model is to verify the predicted growth of large-scale structure with time. Intriguingly, many recent measurements have reported small discrepancies in such tests of structure growth ("the S8 tension"), which could hint at systematic errors or even new physics. Motivated by this puzzling situation, I will present new determinations of cosmic...
In the late 1998, SN 1998bw, the supernova associated with GRB 980425, catapulted the collapsar engine (caused by the collapse of a massive rotating star to a black hole) to the top of the list of proposed engines for these cosmic explosions. Another engine argues that the collapse of a massive star to a magnetar could also produce these GRBS. The rarity of these events argues that only a...
We develop a framework to compute the tidal response of a Kerr-like compact object in terms of its reflectivity, compactness, and spin, both in the static and the frequency-dependent case. Here we focus on the low-frequency regime, which can be solved fully analytically. We highlight some remarkable novel features, in particular: i) Even in the zero-frequency limit, the tidal Love numbers...
The ESA Gaia astrometric mission has revolutionized our understanding of the Milky Way (MW) by providing six-dimensional phase-space measurements of its stars. Utilizing the third data release (Gaia DR3), we have derived a precise MW rotation curve (RC) extending up to 26.5 kpc. For the first time, we detect a Keplerian decline in the RC from 19 to 26.5 kpc. We estimate the MW dynamical mass...
Although astronomers quickly identified stellar implosion as the dominant progenitor of long-duration gamma-ray bursts, the exact mechanism that produces the high angular momenta in the progenitor that is required to produce gamma-ray bursts. The properties of the supernovae associated with these bursts (currently believed to be primarily/all type Ic supernovae) provide key insight into the...
With the IXPE satellite a new observational window has opened for the study of the physical properties of Pulsar Wind Nebulae. For the first time we are able to directly map the magnetic field geometry in the inner regions of these systems, where our current theoretical models place the site of particle acceleration. I will review the current status of X-ray polarimetry in PWNe, in the context...
Micro-Hertz Gravitational Waves (0.1-100 Hz): Overview of Sources and Detection Methods
Wei-Tou Ni and Gang Wang
The micro-Hz GW (Gravitational Wave) band, ranging from 0.1 to 100 Hz, occupies a crucial intermediate gap between the PTA (Pulsar Timing Array) GW detection band (0.03—100 nHz) and the sensitive bands of space missions like LISA/Taiji/TianQin (0.1 mHz—1 Hz). This frequency...
The deployment of large sky surveys are enabling the characterization of the transient night sky in unprecedented detail. Among other things, such surveys are revealing novel modes of variability around supermassive black holes which are incompatible with the behaviour of active galactic nuclei.
This includes quasi-periodic X-ray eruptions, or QPEs, which repeat on timescales of hours-days...
We investigate inflationary particle production, focusing in particular on the role of inflaton fluctuations and the corresponding geometric particle production arising from spacetime perturbations. We analyze both small and large-field models, in agreement with experimental observations, also discussing nonminimal coupling to the scalar curvature of spacetime. Geometric production is then...
In recent work [1,2] we have shown that within the natural warm inflationary paradigm (WNI) observational constraints on the primordial power spectrum from the cosmic microwave background (CMB) can be satisfied without going beyond the Planck scale of the effective field theory. Moreover, WNI can inevitably provide perfect conditions for the production of primordial black holes (PBHs) in the...
The high-energy neutrino observatory ANTARES concluded its 15-year observational campaign in February 2022. Among is primary goals was the identification of the sources of cosmic neutrinos.
Throughout its operational lifespan, ANTARES conducted multiple searches aimed at detecting steady and transient neutrino sources using different methods, such as inspecting for possible neutrino...
Using a new sample consisting of 264 GRBs with measured redshifts and spectra, we applied different techniques to calibrate the Ep,I-Eiso correlation against the type Ia SN data to build a calibrated GRB Hubble diagram. We tested the possible redshift dependence of the correlation and its effect on the Hubble diagram to investigate the tension with the flat ΛCDM model and the dark energy...
Gravitational waves propagate at the speed of light. If we take an ultra-short distributional pulse of gravitational radiation, the resulting wavefront will move along a co-dimension one light-like (null) surface in spacetime. The question of how to describe the quantum geometry of such impulsive null initial data is an important physical problem shared across different approaches. In my...
I observe that some of the key challenges faced by quantum-gravity research, and particularly by quantum-gravity phenomenology, can be traced back to grey area of our understanding of the interface between quantum mechanics and special relativity
In twelve years on the International Space Station, AMS has collected more than 230 billion cosmic rays up to energies of multi-TeV. The precision of the magnetic spectrometer enables us to present data to an accuracy of ~1%. Explicitly, the high energy data on elementary particles (electrons, positrons, antiprotons, and protons) requires new sources of explanation. The data on nuclei and...
Singularities in Newton's gravity, in general relativity (GR), in Coulomb's law, and elsewhere in classical physics, stem from two ill conceived assumptions that, a) there are point-like entities with finite masses, charges, etc., packed in zero volumes, and b) the non-quantum assumption that these point-like entities can be assigned precise coordinates and momenta. In the case of GR, we argue...
Ultra-long period (ULP) radio transients are one of the most recent mysteries in compact object astrophysics. Theories suggest that these could be slowly spinning neutron stars or white dwarfs. However, the confirmation of either (or both) would be a giant leap toward understanding the evolution of compact objects and the physics of coherent radio emission. This has led to large-scale...
The ESA Euclid mission will conduct an extragalactic survey over about 14 000 deg2 of extragalactic sky. The two instruments onboard, VIS and the Near-Infrared Spectrometer and Photometer (NISP), will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy over the survey footprint. In addition to accurate weak lensing and clustering measurements that probe...
On behalf of the SVOM collaboration, I will present the science objectives, characteristics and status of the Chinese-French Space-based multi-band astronomical Variable Objects Monitor mission, expected to put in orbit, at the end of June 2024, a spacecraft carring four instruments, working in a range from visible to gamma-ray frequencies, in order to observe transient and variable...
We use the formalism of geometrothermodynamics to associate a Riemannian manifold called equilibrium space to any thermodynamic system. In the case of an ideal gas, we show that quasi-static thermodynamic processes correspond to geodesics in the equilibrium space. Interpreting time as the affine parameter along geodesics, we show that the entropy of the ideal gas is linearly proportional to...
The ESA INTEGRAL satellite, devoted to high resolution spectroscopy coupled to good imaging capabilities over a wide field of view in the 15 keV - 10 MeV range, was launched in October 2002. After more than two decades, its four instruments are still working well, and they provide unique capabilities in the study of high-energy phenomena.
In this talk I will give a brief overview of the...
A two scalar field model that incorporates non Riemannian Measures of integration or usually called Two Measures Theory (TMT) is introduced, in order to unify the early and present universe. In the Einstein frame a K-essence is generated and, as a consequence for the early universe, we can have Inflation and then subsequent early and present present dark epochs with consistent generation...
We present high-statistics measurements of primary cosmic rays, including Proton, Helium, Carbon, Oxygen, Neon, Magnesium, Silicon, Sulfur, Iron, and Nickel, based on 11.5 years of AMS data. The data reveals, with high accuracy, that there are only three distinct classes of primary elements. Additionally, we provide a systematic comparison with the latest GALPROP cosmic ray model.
The relationship between philosophy and science has historically been characterized by a deep interconnection between the empirical construction of reality and theoretical frameworks. Physics, as an epistemologically autonomous discipline with its own experimental scientific method, has its roots in philosophical reflection on natural phenomena. However, in today's educational system, science...
Cosmology is mainly based on the Friedmann's equations assuming Isotropy and Homogeneity of the Einstein spacetime, starting from the Friedmann-Lemaître-Robertson Walker metric. Introduction of an ad hoc Cosmological Constant allows to model phenomenologically the so-called Dark Energy for explaining the acceleration of the Universe expansion discovered by Riess et al. and Permutter et al....
Supernova remnants (SNRs) are among the most important sources of non-thermal X-rays in the sky and likely contributors to Galactic cosmic rays and represent ideal targets to showcase the capabilities of the Imaging X-ray Polarimetry Explorer (IXPE) in performing spatially-resolved X-ray polarimetry.
For the first time, we can determine the turbulence level (through the measurement of...
In this talk, I will discuss the probability distribution of the spins of primordial black holes (PBHs) formed in a matter-dominated universe. For this evaluation, I focus on cosmological perturbations that follow a Gaussian distribution and examine their linear-order effects on the tidal torque they generate. By the time the fluid gravitationally collapses to form a PBH, nonlinear effects...
SVOM (Space-based multi-band astronomical Variable Objects Monitor) is a Sino-French mission launched in June 2024. Its Core Program is dedicated to the detection and study of Gamma-Ray Bursts (GRBs). I will show how the set of SVOM instruments as well as the observing strategy compare with previous mission, and present how SVOM allows new discovering space and how it will improve GRB studies.
Tidal disruption events (TDEs) are one of the most dramatic nuclear transients in which a star is destroyed by the intense tidal force of supermassive black holes in a few hours, generating a flare luminous enough to outshine the entire host galaxy. Since its first detection in the 1990s, the number of detected events have been steadily growing thanks to ongoing surveys and telescopes, such as...
The nature of recently discovered ultra-long period radio transients is uncertain. If these sources are neutron stars, their long periods strongly challenge rotation-powered emission models. In this talk, I will present a new model of radio emission from ultra-long period magnetars, in which crustal stresses power magnetospheric twists, which dissipate to produce coherent radio emission. I...
KM3NeT is a multi-site underwater detector, designed to detect and study cosmic neutrinos and their sources in the Universe, and improve the measurement of the neutrino oscillation parameters. Two neutrino telescopes are under construction in the Mediterranean Sea, ARCA (Portopalo di Capo Passero, Italy) and ORCA (Toulon, France), optimized respectively for neutrinos in the energy range of 1...
Coalescing supermassive black hole binaries (SMBHBs) are the primary source candidates for low frequency gravitational wave (GW) detections, which could bring us deep insights into galaxy evolutions over cosmic time and violent processes of spacetime dynamics. Promising candidates had been found based on optical and X-ray observations, which claims for new and ready-to-use GW detection...
It is a longstanding conjecture that spacetime is emergent from an unknown substructure on an ultramicroscopic scale. While there are many competing models of this sort, a generic question is whether the existence of a fundamental length has any observable consequences. To investigate this, we have examined various quantum field effects within the framework of one such model: Doubly Special...
In this talk we present the analysis of the embedding of a large class of generalized LTB models in effective spherically symmetric spacetimes. We introduce a reconstruction algorithm that allows, for a large class of models, to construct from a given metric in Schwarzschild-like coordinates the corresponding effective spherically symmetric model, its dynamics as a 1+1-dimensional field...
I will review what the perspectives of quasars in the context of observational cosmology are and I will present recent measurements of the expansion rate of the Universe based on a Hubble diagram of quasars detected up to the highest redshift ever observed (z~7.5). A deviation from the ΛCDM model emerges at higher redshift, with a statistical significance of ~4σ. If an evolution of the dark...
ESA's mission Euclid launched in July 2023 was fully commissioned and since early 2024 is performing its nominal survey. Euclid performs an extra galactic survey (0<z<2) using visible and near-infrared light. To detect infrared radiation is equipped with the Near-Infrared Spectro-Photometer (NISP) instrument sensible in the 0.9-2 µm range. The NISP instrument will be extensively described,...
Remnants of binary black-hole mergers can gain significant recoil or kick velocities due to the anisotropic emission of gravitational waves, which may leave a characteristic imprint in the observed signal. So far, only one gravitational-wave event supports a non-zero kick velocity: GW200129_065458. This signal is also the first to show evidence for spin-precession. For most other...
There is solid theoretical and observational motivation behind the idea of scale invariance as a fundamental symmetry of Nature. We consider a recently proposed classically scale-invariant inflationary model, quadratic in curvature and featuring a scalar field nonminimally coupled to gravity. We go beyond earlier analytical studies, which showed that the model predicts inflationary observables...
In this talk I will describe novel techniques to simulate the nonlinear collapse of dark matter in the cosmos. I will then present simulations of the abundance of dark matter halos and subhalos as a function of the properties of dark matter. In addition, I will discuss simulations that focus on the first collapse of dark matter haloes and the emergence of single power law density profiles....
In this talk various definitions and realizations of time are considered and compared. These realizations are clocks based on kinematics and dynamics, on electromagnetic and gravitational interactions, on classical and quantum systems. Conditions are stated for which all these time scales coincide. Furthermore, the issue of the synchronization of clocks will be treated. Finally, the importance...
We present high-statistics measurements of the secondary cosmic rays Lithium, Beryllium, Boron, and Fluorine based on 11.5 years of AMS data. The unexpected rigidity dependence of the secondary cosmic ray fluxes and their ratios to the primary cosmic rays such as Li/C, Be/C, B/C, Li/O, Be/O, B/O, F/Si and P/Si are discussed. The systematic comparison with the latest GALPROP cosmic ray model is...
To describe the dark side of the Universe, we adopt a novel approach where dark energy is explained as an electrically charged majority of dark matter. Dark energy, as such, does not exist. The Friedmann equation at the present time coincides with that in a conventional approach, although the cosmological "constant" in the Electromagnetic Accelerating Universe (EAU) Model shares a time...
Quasi-periodic eruptions (QPEs) are an emerging class of high amplitude bursts of X-ray radiation, repeating on a hours-day timescale, recently discovered near the central supermassive black holes (SMBHs) of a few low-mass galaxies. I will briefly review our current theoretical understanding of QPEs, and will focus on a scenario involving a main-sequence star repeatedly colliding with an...
The first spectral images of the environment surrounding SgrA* suggested the co-existence of thermalized plasma with extended regions showing the typical spectrum of a “cold” matter irradiated by a flux of hard X-Ray. In 2002 E.Churazov, R.Sunyaev and S.Sozonov proposed to measure the polarization of this reflected component in the brightest molecular cloud around the Galactic Center, SgrB2,...
We find an exact time-dependent instanton solution on a vacuum Kerr-like warped spacetime in conformal dilaton gravity. The antipodal boundary condition on the hypersurface of a Klein bottle $\sim \mathbb{C}^1\times\mathbb{C}^1$ is used to describe the Hawking particles. We used the Hopf fibration to get $S^2$ as the black hole horizon, where the centrix is not in a torus but in the Klein...
We present a sample of 99 dwarf galaxies (stellar mass < 10^9.5 M⊙) with X-ray activity in their central regions. The sample was obtained from a match of the SRG/eROSITA X-ray catalogue in the eastern galactic hemisphere with the MPA-JHU SDSS catalogue. The obtained matches were cleaned rigorously with the help of external optical catalogues to increase the purity of the sample. This work is...
The recently launched SVOM (Space-based multi-band astronomical Variable Objects Monitor) mission is a French-Chinese collaboration dedicated to the study of high energy transients, particularly gamma-ray bursts (GRBs). Boasting sensitivity from gamma-ray to optical wavelengths, SVOM will have the ability to promptly localize GRBs to arcminute precision and provide rapid optical follow-up from...
We investigate the implications of decoherence induced by quantum spacetime properties on neutrino oscillation phenomena. We develop a general formalism where the evolution of neutrinos is governed by a Lindblad-type equation and we compute the oscillation damping factor for various models that have been proposed in the literature. Furthermore, we discuss the sensitivity to these effects of...
The binary-driven hypernova (BdHN) model proposes long gamma-ray bursts (GRBs) originate in binaries composed of a carbon-oxygen (CO) star and a neutron star (NS) companion. The CO collapse triggers the GRB. It generates a newborn NS ($\nu$NS) and a supernova (SN) that accretes onto the NS and the $\nu$NS. This accretion process, which is highly super-Eddington, rapidly transfers mass and...
To address the problem of time in canonical quantum gravity, one strategy is to use relational observables which results in the use of reference fields or clocks. We explore various ramifications of these clocks in the classical as well as quantum setting. First we show the way the choice of clocks is tied to gauge fixing and gauge invariant variables in the classical cosmological...
The contribution is focused on the description of the VIS instrument onboard the ESA Euclid mission. VIS is a large optical-band imager with a field of view of 0.54 deg^2 and a spatial resolution of 0.18". It will be used to survey approximately 14,000 deg^2 of extragalactic sky to measure the distortion of galaxies in the redshift range z=0.1-1.5 resulting from weak gravitational lensing, one...
KM3NeT is the next generation deep-sea neutrino telescopes currently under construction in the Mediterranean Sea. It is composed of two water-Cherenkov neutrino detectors: ARCA and ORCA, located at two sites, south-est of Portopalo di Capo Passero (Italy) and close to Toulon (France), respectively. One of the main scientific goals of KM3NeT is to observe cosmic neutrinos and investigate their...
I will present the quantum evolution of scalar field modes on a quantum spacetime of a collapsing, homogeneous dust ball. Without field backreaction, quantum gravity resolves classical singularities, causing a bounce on the collapse background. Including backreaction, the emergent dressed geometry becomes mode-dependent, resembling a radiation fluid. I will examine the semiclassical dynamics...
Cosmic ray acceleration inside compact star clusters has recently received much attention, mainly because of the detection of gamma ray emission from some of such astrophysical sources. Here we focus on the acceleration of nuclei at the wind termination shock and we investigate the role played by proton energy losses and spallation reactions of nuclei, especially downstream of the shock. We...
In this talk I will make the case that ultra-long period radio pulsars are magnetically powered neutron stars, or magnetars in the broadest sense of the term. Although they appear very different observationally from X-ray magnetars, I will argue they host strong magnetar-like fields. This will encompass arguments from many directions, including source densities, energetics, the physics of how...
Singularities in Newton's gravity, in general relativity (GR), in Coulomb's law, and elsewhere in classical physics, stem from two ill conceived assumptions that, a) there are point-like entities with finite masses, charges, etc., packed in zero volumes, and b) the non-quantum assumption that these point-like entities can be assigned precise coordinates and momenta. In the case of GR, we argue...
In the standard cosmological model the dark matter (DM) particles are collisionless and, because of this very nature, they develop halos with the characteristic central cusp known as NFW profile. Real galaxies do not show NFW profiles but, rather, have a DM mass distribution with a central plateau or core, characteristic of self-gravitating systems in thermodynamic equilibrium (SA+20). Within...
Effective field theory methods have been used in a multitude of applications in gravitational theory, and recent efforts employ such techniques to study tidal interactions. The tidal deformability of stars presents exciting opportunities to analyze both nuclear and gravitational physics due to its dependence on the interior physics of stellar bodies. Information about tidal deformability is...
Most observed binary black hole (BBH) mergers belong to the stellar-mass BBH population produced by the collapse of isolated stars. A pair-instability supernova (PISN) mechanism prevents the formation of black holes from the stellar collapse with mass greater than 50 and less than 120 solar masses. Any BBH merger with a component black hole in the PISN mass gap is likely to originate from an...
We revisit basic problems of classical Friedmann-Lemaître cosmology that motivate the idea of cosmological inflation in light of modern ideas on quantum geometry. Classical cosmology assumes the validity of General Relativity with its smooth Riemannian spacetime geometry at all scales, even below the Planck scale where quantum-gravitational effects are expected to dominate. We argue that...
Quasi Periodic Eruptions (QPEs) are a puzzling X-ray phenomena
recently discovered in a number of sources with similar properties.
In this talk, I am going to present a theoretical model that is able
to reproduce their phenomenology in at least 4 sources. The QPEs
arise from impacts between an Extreme Mass Ratio Inspiral (EMRI)
object and a rigidly precessing TDE-like accretion...
I observe that some of the challenges faced by quantum-gravity research can be traced back to the conceptual tension between relativity and quantum mechanics
It is a fact that the universe lives on a gravitational wave background (GWB), which is extra space–time energy that is not contained in Einstein’s field equations. In a previous work, this energy is treated as a property of space–time and not as a source. With this in mind, a new model was developed that incorporates this energy to explain the current accelerated expansion of the universe...
SOXS (Son Of X-Shooter) will be a unique spectroscopic facility built by an international consortium for the ESO-NTT 3.6-m telescope in La Silla (Chile). The design foresees a single-object, high-efficiency spectrograph with a resolution-slit product of ~ 4,500, capable of simultaneously observing the complete spectral range 350 - 2000 nm with a good sensitivity and with imaging capabilities...
Since the seminal work of Jacobson, it has been known that the equations governing gravitational dynamics can be reconstructed from thermodynamics of local causal horizon. Remarkably, it is even possible to recover low energy quantum phenomenological corrections to gravitational dynamics from thermodynamics. In vacuum, the only possible such corrections are quadratic in Weyl tensor. These...
The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main components, dark matter and dark energy, remains unknown. The Euclid mission will provide high-resolution optical imaging, along with near-infrared imaging and spectroscopy, covering approximately 14,000 square degrees of extragalactic sky. Euclid is optimized for two powerful...
We present the Imaging X-ray Polarimetry Explorer (IXPE) observation of the gamma-ray burst (GRB) 221009A, which reached Earth on October 9, 2022. Although IXPE was not originally designed for this purpose, the exceptional brightness of GRB 221009A allowed it to observe the afterglow emission even after almost 60 hours, providing the first constraints on the X-ray polarization in the 2-8 keV...
Extracting nonlinear nature of astrophysical systems, particularly
from observed data, has long been considering for various kinds of sources.
Accretion disks around compact objects are one of them. Our group
has been working on it for more than two decades: for GRS 1915+105,
Sco X-1, Cyg X-1,2,3, IGR J17091–3624, etc. Sources exhibit sometimes
chaotic/deterministic and sometimes...
Gravitational waves provide a unique probe to physics in strong gravity regime and dark sector of our universe. In this talk, we will discuss the effects of ultralight fields on binary inspirals, assuming the fields are significantly excited by neutron stars or black holes in the binaries. We will report on a search for axion-like particles by analyzing the gravitational waves from the binary...
The era of long gamma-ray bursts (LGRBs) and supernovae (SNe) connections started with the discovery of the first direct temporal and spatial connection of GRB 980425 and SN 1998bw. This field has evolved enormously over the last two decades, with more than fifty LGRBs and SNe association events. The association of a SN with a GRB can be seen as a late-time bump in the optical/NIR light curves...
KM3NeT is a deep-sea research infrastructure comprising two water-Cherenkov neutrino telescopes being constructed in the Mediterranean Sea: ARCA in Italy, aiming at identifying and studying TeV-PeV astrophysical neutrino sources, and ORCA in France, designed to study the intrinsic properties of neutrinos in the few-GeV range. KM3NeT is also able to detect MeV-scale neutrinos expected at...
Recent measurements revealed the presence of several features in the cosmic ray spectrum. In particular, the proton and helium spectra exhibit a spectral hardening at ≈ 300 GV and a spectral steeping at ~ 15 TV, followed by the well known knee-like feature at ~ 3 PV. The spectra of heavier nuclei also harden at ~ 300 GV, while no claim can be currently done about the presence of the ~15 TV...
One of principal aspects in which the effects of quantum gravity are hoped to manifest itself through possible modification to a dispersion relation of electromagnetic (e-m) waves. By combining (i) the symmetry reduced approaches to spacetime quantization, including loop quantum cosmology or geometrodynamics framework, and (ii) the (extension of the) Born-Oppenheimer approximation of...
The present-day standard model of cosmology, Lambda-CDM, gives us a representation of a cosmos whose dynamics is dominated by gravity (general relativity) with a finite lifetime, large scale homogeneity, expansion and a hot initial state, together with other dark elements necessary to avoid certain inconsistencies with observations. There are however some models with characteristics that are...
In general relativity, the use of conformal transformation is ubiquitous and leads to two different frames of reference, known as the Jordan and the Einstein frames. Typically, the transformation from the Jordan frame to the Einstein frame involves introducing an additional scalar degree of freedom, often already present in the theory. We will show that at the quantum level, owing to this...
Recently discovered long-period pulsars (LPPs), namely PSR J0901–4046 (76 s), GLEAM-X J162759.5–523504.3 (1091 s), and GPM J1839–10 (1318 s), have rotational periods much longer than those of radio pulsars and other isolated neutron star populations. LPPs exhibit transient pulsed-radio epochs with unusual and variable pulse shapes, similar to the radio behaviors of rotating radio transients...
Recent breakthrough discoveries in multi-messenger astronomy include the first identifications of cosmological neutrino and gravitational wave sources. Among these are well-known gamma/X-ray transient sources such as active galactic nuclei and gamma-ray bursts. Several more identifications are expected over the next decade. However, it will only be in the second half of the 2030s that...
For the first time in the literature, a dark matter (DM) halo model based on first physical principles such as (quantum) statistical mechanics and thermodynamics is used to try to reproduce 6D phase-space observations in stellar streams. We model both DM haloes, the one of the progenitor and the one of its host with a spherical self-gravitating system of neutral fermions which accounts for the...
Observations with the Gaia satellite have confirmed that the satellite galaxies of the Milky Way are not distributed as homogeneously as expected. The same occurs in galaxies such as Andromeda and Centaurus A, where satellite galaxies around their host galaxies have been observed to have orbits aligned perpendicular to the galactic plane of the host galaxy. This problem is known for the Milky...
This preliminary study aims to explore the contrasting X-ray signatures of accretion and ejection processes in supermassive black holes, focusing on both persistent active galactic nuclei (AGN) and transient sources, such as tidal disruption events (TDEs), quasi-periodic eruptions (QPEs), and quasi-periodic outflows (QPOuts). We will examine the continuum emission characteristics, comparing...
To study the historical galactic Supernovae it is necessary the knowledge of the observations made with the naked eye. Within 2' of theoretical angular accuracy in daytime and 1' in nightime, the astronomical observations made before Tycho were conducted artistically, depending on the skills, the techniques available and the inspiration of the astronomers.
Galileo Galilei stands in between...
For galaxy clustering, constraining cosmological parameters using the three-point correlation function, despite being pivotal, has historically been limited by the computational cost of modelling. Here, we introduce a new emulator developed within the framework of a Euclid Preparation Key-Project activity, which substantially accelerates MCMC evaluation. For the first time in a simulation...
We use the state-of-the-art data on cosmic chronometers (CCH) and the Pantheon+ compilation of supernovae of Type Ia (SNIa) to test the constancy of the SNIa absolute magnitude, $M$, and the robustness of the cosmological principle (CP) at $z<2$ with a model-agnostic approach. We do so by reconstructing $M(z)$ and the curvature parameter $\Omega_{k}(z)$ using Gaussian Processes. Moreover, we...
Cosmic neutrinos are a subdominant part of the cosmological dark matter whose main cosmological effect is to suppress the small-scale clustering. This has enabled an upper limit on the sum of their masses to be placed from astronomical data, with at most 2\% of the dark matter composed of neutrinos at 95\% confidence, or $\Sigma m_{\nu} < 0.12 ~\rm{eV}$. This bound assumes that the...
Over the last decade the international network of gravitational wave detectors (LIGO-Virgo-KAGRA) have detected close to a hundred compact binary mergers. All observations have been consistent with mergers of black holes or neutron stars, but some have been posited as signals generated by the merger of exotic stars. The signal from any compact binary merger would look like that emitted by the...
Real extreme/intermediate-mass ratio inspiral (E/IMRI) systems are likely to contain large accretion discs which could be as massive as the central supermassive black hole. Therefore, contrary to its ideal model, a real E/IMRI system contains a third important component: the accretion disc. We study the influence of these discs on the emitted gravitational wave (GW) profile and its...
Observationally, it is well established that the masses of central black holes are tightly correlated with galaxy properties, most notably the bulge’s velocity dispersion. Cosmological hydrodynamical simulations can capture most of these correlations, but it is yet not understood why this occurs. To gain greater insight into central black hole growth we use machine learning algorithms to study...
Imaging X-ray Polarimetry Explorer (IXPE), the first dedicated astrophysics mission for X-ray polarimetry, has now completed its 2-year prime mission phase, increasing the number of X-ray polarization detections from one to a few dozen, with significant consequences for our understanding of high-energy astrophysical objects. Radio-loud AGN are one of the prime source classes for IXPE, and I...
In this work, we examine the dynamical aspects of the cosmological Mixmaster model within the framework of a non-commutative Generalized Uncertainty principle (GUP) theory.
The theory is formulated classically by introducing a well-defined symplectic form that differs from the ordinary one, thereby inducing a deformation of the Poisson brackets.
We first investigate the behavior of the ...
We explore the X-ray emission from PSR B1055–52 using observations from XMM-Newton taken in 2019 and 2000. Traditional models of neutron star atmospheres fail to adequately describe the phase-integrated X-ray emission of this pulsar. Instead, our findings suggest a dual blackbody model with differing temperatures and areas, supplemented by a nonthermal power-law component, fits best. Our...
I review the phenomenology of Planck-scale effects influencing the propagation of high-energy particles from astrophysical sources.
I discuss the interplay between Planck-scale effects and the universe expansion, and present possible methods to constrain such effects using observations.
On August 17, 2017, the joint detection of GW170817 and GRB 170817A opened the era of multi-messenger astronomy with gravitational waves (GWs) and provided the first direct probe that at least some binary neutron star (BNS) mergers are progenitors of short gamma-ray bursts (S-GRBs). Since then, no other joint BNS/S-GRB observations have been reported. On May 2024 the fourth LVK observing run...
In this talk I will present the evolution of perturbations in a sub-class of Horndeski models characterised by shift symmetry, considering a very general parametrisation of the background. I will show how the free background parameters affect the evolution of the perturbations and present results on the halo mass function and how we can use it to distinguish these models from the standard LCDM...
Detection, observation, and description of supernovae associated with gamma-ray bursts are currently topical tasks in the field of transient phenomena. However, there is a certain pool of factors that can complicate or even make it impossible to identify a supernova in the light curve of a gamma-ray burst. And even if a supernova signature has been detected, further steps to determine its...
Electron capture (EC) decay relies on attachment and stripping cross-sections, that in turn, depend on the atomic number of the nucleus. We revisit the impact of EC decay in the context of the high-precision cosmic-ray fluxes measured by the AMS-02 experiment. We derive the solution of the steady-state fluxes in a 1D thin disk model including EC decay. We compare our results with relevant...
Observations by Planck indicate that CMB anisotropies are consistent with predictions of nearly Gaussian primordial perturbations as the one generated in slow roll inflation. On the other hand, loop quantum cosmology (LQC) generates a non-Gaussian bispectrum. In particular, calculations of primordial bispectrum generated in LQC shows that the non-Gaussianity function $f_{_{\rm NL}}(k_1,\,...
In the Universe, the nucleosynthesis beyond iron group elements occurs thanks to neutron capture processes. In the context of the multi-messenger astronomy, the observation of the electromagnetic (EM) counterpart of the GW170817 event, known as kilonova (KN), provided evidence that the coalescence of binary neutron stars systems is a favourable stellar site hosting the rapid neutron capture...
Precision measurements of the cosmic ray D flux are presented as function of rigidity from 1.9 to 21 GV, based on 21 million D nuclei. We observed that over the entire rigidity range D exhibit nearly identical time variations with p, ${}^{3}$He, and ${}^{4}$He fluxes. Above 4.5 GV, the D/⁴He flux ratio is time independent and its rigidity dependence is well described by a single power law ∝...
The radio pulsar PSR J0901-4046 exhibits very slow rotation with a spin period
76 s, which is unusually low for a neutron star. Typically the spin period of
radio pulsars ranges 1.4 ms to 23.5 s, when they are divided into various
sub-classes, e.g. transient, millisecond pulsar, magnetar. The question
arises, is PSR J0901-4046 really a neutron star? In fact, the spin period
76 s more...
The future Euclid space satellite mission will offer an invaluable opportunity to constrain modifications to general relativity at cosmic scales.I will present forecasts for extended cosmological scenarios such as k-mouflage gravity and the Transitional Planck Mass model, considering spectroscopic and photometric primary probes by Euclid alone and in combination with other probes. In...
This work aims to investigate the impact of spatial curvature in modified gravity models, specifically within the Horndeski framework. Typically overlooked in the literature due to the spatial flatness assumed in the ΛCDM model, this study aims to fill this gap. The ΛCDM model, rooted in General Relativity (GR), is in good agreement with observational data, but faces problems with cosmological...
The collapse of a spherically symmetric ball of dust has been intensively studied in Loop Quantum Gravity (LQG). From a quantum theory, it is possible to recover a semiclassical regime through a polymerization procedure. In this setting, general solutions to the Polymerized Einstein Field Equations (PEFE) will be discussed both for the interior and the exterior of the dust cloud. Exterior...
ASTROD-GW is designed to observe gravitational waves in the micro-Hz frequency band, employing three spacecraft near the Sun–Earth Lagrange points L3, L4, and L5 to form triangular interferometers with a 2.6 AU arm length. Benefiting from the relative gravitational stabilities of the Lagrange points in 30 years, the mission orbit can remain stable for more than 10 years. The antenna pattern of...
In this talk I will show that the theoretical model of physical black holes predict that gravitational wave echos acoompanies with all the black hole merger events in real world. The first part of my talk will be introducing the concept of physical black holes, highlighting that all the black holes in observed in astronomy should be discribed by dynamical, horizonless and singular free metric....
Recently, a previously quiescent nearby galactic nucleus, ASASSN-20qc, went to an outburst during which it has shown quasioperiodic ultra-fast outflows (qUFOs) with changing column density every cca 8 days. Different physical mechanisms have been proposed to explain such behaviour, with the most promising scenario being the smaller, probably intermediate-mass black hole, orbiting the primary...
The particles ejected from the Sun during some particularly powerful eruptions (X-ray flare class X) reach the Earth in twenty minutes, immediately after the photons that carry the image and information of the event.
The speed of the most energetic protons of the solar wind is measurable from the images of C3 coronagraph of SOHO SOlar and Heliospheric Observatory and from the X-ray and proton...
MAGIC is an imaging atmospheric Cherenkov telescope that has been observing very high energy gamma rays above 100 GeV for over 20 years. Thanks to its location and low energy threshold, MAGIC is particularly well-suited for observing blazars. Its observation strategy combines the monitoring of a few selected sources with the observation of new targets, often triggered by Target of Opportunity...
GRB 210704A is a burst of intermediate duration (T90~1-4 s) followed by a fading afterglow and an optical excess that peaked about 7 days after the explosion. Its properties, and in particular those of the excess, do not easily fit into the well established classification scheme of GRBs as being long or short.
In this talk, I will present multi-wavelength observations of the GRB and its...
Using Low Brightness Surface Galaxies (LBSG) rotational curves we inferred the free parameters of l-boson stars as a dark matter component. The l-boson stars are numerical solutions to the non-relativistic limit of the Einstein-Klein-Gordon system, the Schrödinger-Poisson (SP) system. These solutions are parametrized by an angular momentum number l = (N −1)/2 and an excitation number n. We...
We investigate the quantum speed limit (QSL) during the time evolution of neutrinos and antineutrinos under the influence of a gravitational field. We derive an analytical expression for the four-vector gravitational potential in the underlying Hermitian Dirac Hamiltonian using the Boyer-Lindquist coordinates. This gravitational potential leads to an axial vector in the Dirac equation in...
We investigate the massless scalar field perturbations, including the quasinormal modes spectrum and the ringdown waveform, of regular black hole spacetimes derived within the Asymptotic Safety program. In particular, we discuss the stability of a new class of AS black holes recently derived dynamically within a non-singular model of collapse and explore the possibility of detecting signatures...
Since the very first observations, the Cosmic Microwave Background (CMB) has revealed on large scales unexpected features known as anomalies, which challenge the standard $\Lambda$ cold dark matter ($\Lambda$CDM) cosmological model. One of these is the hemispherical power asymmetry, i.e. a difference in the average power on the two hemispheres centered around (l, b) = (221, −20), which shows a...
In previous work [1] it was shown that a crossover transition from hadronic to quark matter during the merger of neutron stars can lead to interesting observational consequences in the emergent gravitational radiation. In particular, the increased pressure in the crossover density region ($2-5$ times the nuclear saturation density) can lead to an extended duration of high frequency ( $\sim...
Recent remarkable discoveries, such as Einstein’s gravitational waves, “impossible early” galaxies and quasars, 2D photon Bose-Einstein condensate with rest energy etc. provide a solid experimental and observational basis for “fiery marriage of general relativity with quantum theory” (J.Wheeler).
Consecutively, in a physical logic, nature inspire us that primordial black holes (PBHs)...
1E 161348-5055 (1E 1613), the source at the center of the supernova remnant RCW103, has defied any easy classification since its discovery, owing to its long-term variability from months to years and a periodicity of 6.67 hr with a variable light curve profile across different flux levels. On June 2016, 1E 1613 emitted a magnetar-like millisecond burst of hard X-rays, accompanied with a factor...
The precision measurement of daily proton fluxes with AMS during twelve years of operation in the rigidity interval from 1 to 100 GV is presented. The proton fluxes exhibit variations on multiple time scales. From 2014 to 2018, we observed recurrent flux variations with a period of 27 days. Shorter periods of 9 days and 13.5 days are observed in 2016. The strength of all three periodicities...
We consider the gravitational field outside a static, spherically symmetric source in the context of a general $f(R)$ extension of General Relativity. We study the modified Einstein equations (EE), which involve the two free potentials of the metric together with $f(R)$ and its derivative $\phi = \frac{\partial f}{\partial R}$, without making any preliminary assumption on $f$ as a function of...
Effective models of gravitational collapse in loop quantum gravity for the Lemaître-Tolman-Bondi spacetime predict that collapsing matter reaches a maximum finite density, bounces, and then expands outwards. I explain how in the marginally bound case, shell-crossing singularities commonly occur for inhomogeneous initial profiles of the dust energy density; this is the case in particular for...
Euclid is an ESA survey mission designed to understand the origin of the Universe's accelerating expansion using weak gravitational lensing and redshift clustering as main probes. Very high image quality is required for galaxy shape measurements, while accurate photometry at visible and near-infrared wavelengths and near-infrared spectroscopy are needed to measure photometric and spectroscopic...
In this presentation, we discuss a treatment of Casimir-Polder gravitational fluctuation forces based on a classical general relativistic gravitational field framework. In analogy with the acoustic Casimir effect, we analyze the interaction between high density neutron star surfaces within a bath of classical gravitational waves. We extend a previously published treatment of the interaction...
Existence of naked singularities is a topical and fundamental issue of physics. The formation mechanism of such objects, particularly those with near-solar-mass, is not yet clear. Since, recent gravitational wave events have suggested the existence of near-solar-mass collapsed objects which cannot be formed via stellar evolution, here we investigate a likely formation channel, and especially...
The recently reported transient event ASASSN-20qc (Pasham et al., 2024), which was revealed first by the optical outburst and then the delayed soft X-ray emission, was shown to exhibit a quasiperiodic ultrafast outflow. I will show using analytical as well as numerical calculations (see also the contribution by Petra Sukova) that such a behaviour is consistent with the intermediate-mass black...
A panorama of the current historiography on the Supernova of 1054 is outlined. Shklovsky (1968), and Murdin (1985) show how the interpretation of this phenomenon converged on a Su-pernova event. Here we reconsider the historical data, assuming a Gamma-Ray Burst (GRB) as its source. A Supernova correlated with the GRB explains well the fading time observed by the an-cient Chinese astronomers,...
A large number of galactic binary systems emit gravitational waves (GW) continuously with frequencies below ∼10 mHz. The LISA mission could identify tens of thousands of binaries over years of observation and will be subject to the confusion noise around 1 mHz yielded by the unresolved sources. Beyond LISA, there are several missions have been proposed to observe GWs in the sub-mHz range where...
In this work, we study the properties of dissipative shocks for fully relativistic accretion flows around spinning black holes. In an accretion flow harbouring a dissipative shock (formally known as radiative shock), a significant portion of the thermal energy may get released from the post-shock corona. A stellar-mass black hole may therefore emit hard X-rays from the inner edge of the disc....
I will review the theoretical implications of the IXPE and multifrequency polarimetric measurements of the emission from blazars. In particular, for highly-synchrotron peaked BL Lacs current measurements show a strong frequency-dependency of the degree of polarization, commonly attributed to a stratified emission region, possibly associated to shock acceleration. I will discuss this...
There are evidences for neutron stars (NSs) with the rotational frequency of
several 100th of Hz and moderate magnetic fields, though magnetars are slowly
spinning. Hence, if their magnetic and rotating axes are misaligned (nonzero
obliquity angle), hence they are pulsars, then they should be potential
sources for continuous gravitational waves (CGWs), along with their...
In this talk, I will present and discuss the evidence for an off-axis jet in the nearby broad-lined SN 2020bvc. Particular attention will be devoted to the modeling of the multi-wavelength late-time emission detected from this event, and on the signatures of cocoon emission in the very early spectra of this event.
Pulsar timing noise is the stochastic deviation of the pulse arrival times of a pulsar away from their long term trend. In the standard two-component crust-superfluid neutron star model, timing noise can be explained as the perturbation of the two components by irregular torques. Interactions between the crust and superfluid cause these perturbations to decay exponentially with a...
The gravitational waves from the binary neutron star merger GW170817 were accompanied by a multiwavelength electromagnetic counterpart, which confirms the association of the merger with a short gamma-ray burst (sGRB). The afterglow observations implied that the event was accompanied by a narrow, ~5°, and powerful, ~1e50 erg, jet. We study the propagation of a Poynting flux-dominated jet within...
In spherical symmetry, the gravitational potential of galaxies and their halos are univocally derived from the rotational velocity profile. Thousands of galaxies are well-fitted by a universal velocity profile and thus, the gravitational profile is well known. By considering that dark matter can be treated either as an ideal gas, a Fermi, or a Bose gas, we found that only the latter can...
CMB lensing provides a powerful way to measure the mass of the neutrinos. Traditional analyses of CMB lensing can suffer from biases in neutrino mass constraints if the wrong dark energy model or parametrization is assumed. In this talk, I will present a method to remove low-redshift contributions from CMB lensing mass maps, enhancing their sensitivity to high-redshift structures and becoming...
Abstract: Dust is considered to be the simplest form of matter composed of pressureless, radiation and is abundant in galaxies, clusters and superclusters in a cosmological context. It has also been shown that stars are encompassed by these radiating pressureless particles which make up the atmosphere of the star. The gravitational behaviour of these pressureless fluid distributions are...
In this talk, we aim to discuss the abelian features of Loop Quantum Cosmology, demonstrating that the Gauss constraint can be recast into three abelian constraints.
We begin the discussion by considering nondiagonal Bianchi models, illustrating their deep connection with the diagonal case. Specifically, we show that the Hilbert space of these models factorizes into spaces that are isomorphic...
I will present recent lensing results in the massive lensing cluster A2390 which has been observed as part of the Euclid Early Release Observations. The goal is to showcase the weak and strong lensing capabilities of the imaging data of the Euclid satellite.
In the end of 2026, the AMS-02 experiment on the International Space Station will undergo a major upgrade of its apparatus: a double layer of microstrip silicon sensors, for a total area of ~ 7 m^2 and almost doubling the total area of the microstrip silicon tracker, called Layer 0 (L0) will be installed on top of the current flying apparatus.
In this talk we'll present briefly the design and...
It is a fact that the universe lives on a gravitational wave background (GWB). In this talk we start from this hypothesis. Due to the GWB, space-time is fluctuating in such a way that it locally resembles a lake with small waves and therefore quantum particles cannot follow geodesic trajectories, but rather follow stochastic trajectories. In the present talk, we begin by adding a stochastic...
Spherical collapse in general relativity has been studied with different methods, especially by using a priori given equations of state that describe the collapsing matter as a perfect fluid. We propose an alternative perspective, in which the initial density of the perfect fluid is given as a polynomial function of the radial coordinate that is regular everywhere inside the fluid. We then...
The large-scale structures such as Fermi Bubbles and eROSITA Bubbles provide a unique opportunity to study our Milky Way. However, the nature and origin of these large structures are still under debate. In this talk, I will present the identification of several kpc-scale magnetised structures based on their polarized radio emission and their gamma-ray counterparts, which can be interpreted as...
The future space-borne gravitational wave(GW) missions will be able to detect abundant gravitational wave signals in the micro-Hz band. The gravitational wave mission, ASTROD-GW can bridge the gap between the millihertz and nanohertz bands and has a great potential to detect the supermassive black hole binary coalescence events. A large number of galactic binaries will continuously emit GW...
Quantum gravity has yet remained elusive from an observational standpoint. In this talk, I will discuss Swerves, a proposal within quantum gravity phenomenology that predicts testable effects in cosmological data. Motivated by considerations in Causal Set Theory, a discrete approach to quantum gravity, we have formulated the covariant Brownian motion of free particles around their geodesics....
Detecting and interpreting electromagnetic counterparts to binary black hole mergers will require a detailed understanding of the complex plasma dynamics governing the surrounding accretion flow, particularly for binaries including at least one supermassive black hole. Quasi-periodicities observed in active galactic nuclei (AGN) may already provide a clue as to how a secondary black hole in...
The halo of our Galaxy is populated with a significant number of high-velocity clouds (HVCs) moving with a speed up to $500$ km/s. It is suggested that these HVCs might contain a non-negligible fraction of the missing baryons. We aim to estimate the baryonic mass of the Milky Way halo in the form of HVCs to constrain a fraction of missing baryons in the form of these clouds. Such findings...
In this talk I am presenting Bayesian Model Averaging, a well established statistical technique that offers a principled approach to model uncertainty marginalization in a Bayesian context.Specifically, this talk goes through the two recent papers I published in which I describe an implementation of such methodology for Cosmological analyses with 1) an application to the early dark energy as a...
In this talk, I will summarize the results presented during the Parallel session focused on the AMS-02 experiment on the International Space Station, together with their interpretation. In particular, I will discuss the latest flux measurements. The precision of AMS-02 results revealed unexpected phenomena that challenged conventional theoretical models. I will also give a brief overview of...
We have shown earlier that quantum gravity can be described in terms of wave functions on the bundle of spin connection coefficients over spacetime. The corresponding precanonical quantization procedure introduces, for dimensional reasons, an ultra-violet parameter $\varkappa$ of dimension of the inverse 3-volume element. For scalar and Yang-Mills fields, the standard Schroedinger functional...
In the era of big data, developing robust methods for the autonomous extraction of information from vast multi-dimensional datasets is pivotal. This work focuses on utilizing a region-based convolutional neural network (Mask R-CNN) to automatically detect bright arcs produced by strong gravitational lensing in galaxy clusters, specifically for the upcoming Euclid survey. These kinds of events...
A common criticism to deparametrised quantum gravity formalisms, where a time variable is selected before quantisation, is that covariance seems to be lost. In this talk, I will resolve this concern for the group field theory (GFT) approach to quantum gravity thanks to the equivalence between the Dirac quantisation scheme and the Page-Wootters (PW) formalism — applied here to quantum gravity...
We evaluate the effects of repulsive gravity using first order geometric invariants for regular black holes. We compare the repulsive regions with the predictions got from singular solutions. Notable characteristics and pathologies of regular black holes are thus emphasised. To heal the potential incompleteness of regular solutions, we construct alternative regular solutions. Implications and...
The first detection of a binary neutron star merger has made sharp reality the long-standing paradigm that these cosmic fireworks are exciting laboratories for extreme physics. To get the most out of observations, however, we need accurate modelling of the merger dynamics via numerical relativity simulations. In this respect, the large amount of numerical work carried out over the last decade...
Electric and magnetic fields of a charged ring located in the vicinity of Kerr black hole are computed with multipole decomposition. Lines of force of electric and of magnetic fields in the ZAMO frame are presented and analyzed for different positions of the ring and selected values of the Kerr parameter. Special attention is paid to the case when position of the ring approaches the event...
The ordinary atoms that make up the known universe, from our bodies and the air we breathe to the planets and stars, constitute only 5% of all matter and energy in the cosmos. The remaining 95% is made up of a recipe of 25% dark matter and 70% dark energy, both nonluminous components whose nature remains a mystery. Freese will recount the stories of the dark matter puzzle, starting with the...
We will talk about the emergence of new sciences such as “Gravitational-wave astronomy”, “Neutrino extragalactic astronomy”, “Transient radio astronomy”, "Fast Transient X-ray Astronomy".
This map contains information about the diffuse emission of the halo of our Galaxy, millions of accreting supermassive black holes, half a million stars with active coronae, and 50,000 clusters of galaxies filled with dark matter and diffuse hot gas. It demonstrates strong variability of X-ray sources on different time scales from the giant explosions in our Galaxy and the Tidal Disruptions of...
I will briefly discuss how the first images of the supermassive black holes M87 and Sgr A were obtained by the EHT collaboration. In particular, I will describe the theoretical aspects that have allowed us to model the dynamics of the plasma accreting onto the black hole and how the comparison between the theoretical images and the observations on a broad range of frequencies has allowed us...
Launched on January 9th, 2024, the Einstein Probe (EP) is a space X-ray observatory designed to detect mainly high-energy transient and variable sources in the universe. It aims at detecting such sources at unprecedented sensitivity and spatial resolution in the soft X-ray band and performing quick onboard follow-up observations in X-rays. EP carries two instruments, a wide-field X-ray...
In less than two years since the release of the first data, the James Webb Space Telescope has revolutionised our knowledge and understanding of the Universe. Thanks to its unprecedented collecting area and IR sensitivity, JWST has allowed us to study the atmosphere of exo-planeets, stellar populations in nearby galaxies and galaxies and AGNs up to z~15 . In my talk I will review the status of...
We present the seven Episodes characterizing the three most powerful BdHN I. The maximum
energy observed is for GRB 221009A which reaches 1x10 55 erg. New inference for the
explanation of the highest energy radiation in the TeV are presented.
Extreme Mass Ratio binaries are systems containing a massive black hole (>10,000 Msolar) and a closely orbiting smaller object (0.1-1000 Msolar). If the companion is also a compact object they can produce gravitational waves potentially detectable with the space-based detectors that will start operating in the next decade. The identification of electromagnetic counterparts of such...
The eROSITA X-ray satellite has revealed two gigantic bubbles extending to ~80° above and below the Galactic center (GC). The morphology of these ‘eROSITA bubbles’ bears a remarkable resemblance to the Fermi bubbles previously discovered by the Fermi Gamma-ray Space Telescope and its counterpart, the microwave haze. The physical origin of these striking structures has been intensely debated;...
More than a century ago, Albert Einstein presented his general theory of gravitation. One of the predictions of this theory is that not only particles and objects with mass, but also the quanta of light, photons, are tied to the curvature of space-time, and thus to gravity. There must be a critical mass density, above which photons cannot escape. These are black holes. It took fifty years...
The nature of dark matter (DM) is one of the most relevant questions in modern astrophysics. I will present a brief overview of recent results that inquire into a possible fermionic quantum nature of the DM particles, focusing mainly on the interconnection between the microphysics of the neutral fermions and the macrophysical structure of galactic halos. I will show how such an interconnection...
In the early 1960s, as X-ray Astronomy was beginning to take shape, the critical role of X-ray polarimetry became apparent. By 2001, significant progress had been made, demonstrating the effective use of the photoelectric effect in gas as a breakthrough technique in Astrophysics. It wasn't until 2021 that an observatory with the required sensitivity utilizing the photoelectric effect could be...
Located at the China Jinping Underground Laboratory, the PandaX experiment employs xenon as a target to detect rare physics signals, such as dark matter and neutrinos. The PandaX-4T, the latest generation detector featuring a 4-ton xenon target volume, commenced data collection in 2020. One of our objectives is to unravel the nature of dark matter by investigating various potential signatures....
IceCube is a cubic kilometer neutrino observatory at the geographic South Pole whose sensitivity from PeV down to GeV, or MeV using a special DAQ, has spawned a diverse scientific program. It discovered and continues to characterize the astrophysical neutrino flux, recently identifying a galactic component. To resolve it further, IceCube has found a 4.2σ excess from the direction of NGC 1068...
The intersection of General Relativity and geodesy represents a new frontier in Earth sciences. A major task of geodesy is to determine the gravity field of the Earth, e.g. to monitor mass variations. Due to recent advancements in high precision clock comparison, General Relativity introduced an entirely new measurement concept to geodesy based on the gravitational redshift. We present the...
In our quest towards a theory of gravity beyond General Relativity black holes with their strong gravitational fields represent an important testing ground. Among the numerous alternative theories of gravity much work in recent years has focused on a set of scalar-tensor theories, where the scalar field couples to higher curvature terms. The properties of the resulting black holes in such...
The huge luminosity, the redshift distribution extending at least up to z~10 and the association with the explosive death of very massive stars make long GRBs extremely powerful probes for investigating the early Universe (pop-III stars, cosmic reionization, SFR and metallicity evolution up to the “cosmic dawn”) and measuring cosmological parameters. At the same time, GRBs are expected to be...
The advent of a new generation of observational facilities, such as the James Webb Space Telescope (JWST) and the Euclid space telescope, has just inaugurated a new era of discoveries that are destined to revolutionize all fields of astrophysics, including strong gravitational lensing by galaxy clusters. The JWST’s spectrophotometric data, of unprecedented spatial resolution and sensitivity,...
I will first plan to review the accretion phenomenology and underlying
models, mostly for a black hole. I will attempt to touch upon, how over the decades with the evolution of observations with newer data, newer models are proposed to explain them: standard Shakura-Sunyaev Keplerian disk, advective sub-Keplerian disk, magnetically arrested (advective) disk, etc. Finally, I will aim to...
High-energy neutrinos can convey a significant amount of information on the mechanisms at play in astrophysical environments. Neutrino telescopes have been designed to study such signals, detecting the Cherenkov photons induced in deep waters or ice by the charged products of the neutrino interaction. The physics case for neutrino telescopes will be reviewed in this contribution, providing an...
Fast radio bursts (FRBs) are enigmatic millisecond-duration pulses of radio light observed across cosmological distances. Their origins and emission mechanisms remain unclear, making FRBs one of the most intriguing new mysteries in astrophysics. The Canadian Hydrogen Intensity Mapping Experiment (CHIME), with its specialized real-time transient-search engine (CHIME/FRB), has emerged as the...
During the fourth observing run of the LVK collaboration, we have already seen large improvements in the results produced by the search pipelines in low-latency. We have reached new levels of sensitivity and reliability. In the quest to detect every gravitational wave out there, we are now more ready than ever to participate in the next multimessenger event. During this fourth observing run,...
We analyze the extraction of the rotational energy of a Kerr black hole (BH) endowed with a test charge and surrounded by an external test magnetic field and ionized low-density matter. For a magnetic field parallel to the BH spin, the electric field accelerates electrons outward(inward) and protons inward(outward) in a region around the BH poles(equator). For zero net charge, the polar region...
Magnetars are the strongest magnets we know of, with magnetic fields reaching values up to 10^15 G at the surface. Transient activity in the X-/gamma ray regime is the birthmark of magnetars. Their radiative variability includes short, explosive events from milliseconds to hundreds of seconds (i.e., bursts and giant flares) and longer-lived outbursts (weeks to months). In this talk, I will...
Mid-frequency Gravitational Waves (0.1-10 Hz): Overview of Sources and Detection Methods
Youjun Lu and Wei-Tou Ni
The mid-frequency GW (Gravitational Wave) band (0.1-10 Hz) between the 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, GWs can also come from the inspiral phase...
Iron fluorescence emission lines from X-ray binaries and active galactic nuclei are important diagnostic tools for studying the physical processes near the event horizon of both the stellar-mass black holes in X-ray binaries and the supermassive black holes in active galactic nuclei. In this work, we investigate the line profile of the relativistic broad iron lines from the cool accretion disk...
The huge luminosity, the redshift distribution extending at least up to z~10 and the association with the explosive death of very massive stars make long GRBs extremely powerful probes for investigating the early Universe (pop-III stars, cosmic re-ionization, SFR and metallicity evolution up to the “cosmic dawn”) and measuring cosmological parameters. At the same time, as demonstrated by the...
I will review the recent developments of GR MHD numerical simulations of GRB central engines.
I will also present some multi-messenger observational challenges still unsolved by these models.
What has everyone so excited about the H0 tension is the potential for discovering new physics, such as the physics of dark energy. In particular, the question of new physics explanations for this tension are often divided into whether the new physics plays a role at high redshift or low redshift. In this talk, I will make the case that there can be no low-redshift solution to the H0 tension....
Observation of cosmic gamma-rays in the MeV range have long been considered both promising and challenging. The challenges directly result from the physics of the photon-matter interaction at these energies, being dominated by incoherent Compton scattering, forming a global minimum in photon-matter cross-section without an option of building focusing optics. The non transparency of the...
Strange-quark matter (SQM) may be the true ground state of hadronic matter. In this case,the observed pulsars may actually be strange stars, but not neutron stars. According to the SQM hypothesis, the existence of a hydrostatically stable sequence of SQM stars has been predicted, ranging from 1 to 2 solar mass strange stars, to smaller strange dwarfs and even strange planets. While...
The galactic black hole is not very active at present, but at about 1 pc there is a large reservoir of material that will eventually trigger a more intense phase of activity. Smaller-scale processes can also accrete material onto the black hole producing short peaks in activity. Here, I present the structure and dynamics of the interstellar medium from the parsec to sub-parsec scale and how...
This talk presents a new avenue to black hole evaporation using a heat-kernel approach in the context of effective field theory analogous to deriving the Schwinger effect. Applying this method to an uncharged massless scalar field in a Schwarzschild spacetime, we show that spacetime curvature takes a similar role as the electric field strength in the Schwinger effect. We interpret our results...
Most domains of science are experiencing a paradigm shift due to the advent of a new generation of instruments and detectors which produce data and data streams at an unprecedented rate.
The scientific exploitation of these data, namely Data Driven Discovery, requires interoperability, a massive and optimal use of Artificial Intelligence methods in all steps of the data acquisition,...
It is known that all wormholes violate classical energy conditions, non-negativity constraints on contractions of the stress-energy tensor. Since these conditions are violated by quantum fields, it was believed that wormholes can be constructed in the context of semiclassical gravity. But negative energies in quantum field theory are not without restriction: quantum energy inequalities (QEIs)...
Although calculations of QCD thermodynamics from first-principle lattice simulations are limited to zero net-density due to the fermion sign problem, several methods have been developed to extend the equation of state (EoS) to finite values of the $B,~Q,~S$ chemical potentials. Taylor expansion around $\mu_i=0~(i=B,~Q,~S)$ enables to cover with confidence the region up to $\mu_i/T=2.5$....
We study the spontaneous breaking of diffeomorphism invariance using the proper-time non-perturbative flow equation in quantum gravity. In particular, we analyze the structure of the UV critical manifold of conformally reduced Einstein-Hilbert theory and study the occurrence of a non-trivial minimum for the conformal factor at Planckian energies. We argue that our result can be interpreted as...
The first detection of a gravitational-wave signal emitted by a compact binary coalescence was achieved by the network of two LIGO detectors on September 14, 2015. The event, labelled GW150914, is associated with a binary black hole merger. It ushered the era of GW astronomy, offering a new way to probe our Universe.
Since then, during its first three observing runs, the LIGO-Virgo-KAGRA...
In this talk, I will review the state of the art of dark energy in light of the early Stage IV surveys results.
We study the periapsis shift of a quasi-circular orbit in general static spherically symmetric spacetimes. We derive two formulae in full order with respect to the gravitational field, one in terms of the gravitational mass m and the Einstein tensor and the other in terms of the orbital angular velocity and the Einstein tensor. These formulae reproduce the well-known ones for the forward shift...
Magnetic fields in regions of strong gravity play a crucial role in the explanation of various astrophysical phenomena, such as e.g. the formation and collimation of relativistic jets observed in black hole systems of different mass scales. In this presentation, I will discuss the influence of magnetic fields on dynamical environments of supermassive black holes from both theoretical and...
As current space-based gamma-ray instruments such as Fermi begin to show their age, it is time to think about the next generation and the overall future of gamma-ray astronomy in space. To help start the process, NASA has commissioned the Future Innovations in Gamma-Rays (FIG) Science Activity Group (SAG) to collect information and publish a report identifying future gamma-ray science...
The ground-based gravitational wave (GW) observations discover a population of merging stellar binary black holes (BBHs), which could also be detected by the space-based low-frequency GW detectors, such as LISA, Taiji and Tianqin, in their early inspiral stages. The middle-frequency GW band, a missing link between the high-frequency and low-frequency band, is an important piece for multiband...
Multifrequency polarimetry is emerging as a powerful probe of blazar jets, especially due to the advent of the Imaging X-ray Polarimetry Explorer (IXPE) space observatory.
We study the polarization of High-Synchrotron Peaked (HSP) blazars, where both optical and X-ray emission can be attributed to synchrotron radiation from a population of non-thermal electrons. We adopt an axisymmetric...
Strong gravitational lensing is one of the most promising methods for studying the nature of dark matter. It allows one to detect low-mass dark haloes within the haloes of lens galaxies and along their line of sight, providing a quantitative test of the Cold Dark Matter (CDM) paradigm in a halo mass regime and distances that are not accessible to any other technique. So far, two detections of...
Magnetars are isolated young neutron stars that exhibit the most intense magnetic fields known in the Universe and are characterized by a wide variety of high-energy emissions. The birth of rapidly rotating magnetars is also a promising scenario to power outstanding explosive transients. The formation process of these objects, as well as the origin of their ultra-strong magnetic fields,...
ANTARES was the first neutrino telescope that operated in the deep sea for more than 15 years. From its location in the northern hemisphere, it long represented the largest detector world-wide with a privileged view towards the Galactic center, providing valuable results in a variety of investigations. It also served as a long-term, real-time, high-bandwidth facility for sea and Earth science...
This presentation explores some applications of transfer learning in astronomical image analysis, focusing on the usage of a pretrained network (EfficientNet) as a feature extractor. We discuss methods for identifying active galactic nuclei, extracting physical parameters, and detecting anomalies in time series data. Additionally, we present some potential future applications, demonstrating...
TianQin, a space-based gravitational wave (GW) detector scheduled for launch in the mid-2030s, promises groundbreaking insights into the Universe. Operating in the milli-Hertz band, TianQin can detect a diverse array of sources, including double white dwarfs (DWDs), massive black hole binaries (MBHBs), stellar-mass black hole binaries (SBHBs), extreme mass ratio inspirals (EMRIs), and the...
In this talk, I will highlight some of the recent and most exciting theoretical and observational development in gamma-ray bursts (GRBs) that occured in the past decade, alongside some new open questions that I anticipate would be at the forefront of GRB reserch in the next decade. In particular, I will discuss our current state of knowledge on: (1) jet structure, which became evident...
We describe the connection between a traversable wormhole and the Casimir effect. With the help of an equation of state we also discuss different forms of solutions related to the Casimir source. The effect of including an electromagnetic field and a temperature to the original energy density are also discussed.
In the binary-driven hypernova (BdHN) scenario, long gamma-ray bursts (GRBs) originate in a binary system composed of a carbon-oxygen (CO) star and a neutron star (NS) companion in close orbit. The collapse of the CO star generates a newborn NS ($\nu$NS) at its center and a type Ic supernova (SN) explosion. Part of the SN ejecta is accreted onto the NS companion and onto the $\nu$NS by...
We develop a non-conventional description of the vacuum energy in quantum field theory in terms of quantum entropy. Precisely, we show that the vacuum energy of any non-interacting quantum field at zero temperature is proportional to the quantum entropy of the qubit degrees of freedom associated with virtual fluctuations. We prove this for fermions first and then extend the derivation to...
Third generation ground-based gravitational wave detectors will broaden our view of the Universe. In the meantime, upgrade programs as Virgo_nEXT are planned to boost the sensitivity of existing detectors such as Advanced Virgo in the post-O5 time frame. In particular, improving the sensitivity at low frequencies will enable the detection of coalescences of higher mass black holes and allow...
Usually, when we talk about gravitational lensing we either speak of gravitational lensing of light or gravitational waves. However, in the presence of a black hole also massive particles like neutrinos can be gravitationally lensed. While nowadays most neutrino detectors are not sensitive enough to resolve neutrino events with an angular resolution that is high enough so that we can...
The observations of the so-called S-stars together with the dust-enshrouded objects, the G-stars, can help to further corroborate Einstein’s General Relativity theory and to better constrain the nature of the supermassive black hole (SMBH) candidate, SgrA*. In recent years, a novel dark matter (DM) model for galaxy haloes has been developed, the Ruffini-Argüelles-Rueda (RAR) model. It consists...
Fast Radio Bursts (FRBs) are millisecond-duration, bright extragalactic bursts, whose produc- tion mechanism is still unclear. Recently, a persistent radio source (PRS) of non-thermal origin was discovered to be physically associated to two of the repeating FRB sources. These two sources have unusually large Rotation Measure (RM) values, likely tracing a dense magneto- ionic medium, consistent...
The Blandford-Znajek (BZ) mechanism is an electromagnetic manifestation of the Penrose process that currently constitutes the best theoretical candidate to explain the launching of relativistic jets by black holes.
In this talk we offer a modern review about the BZ mechanism and the analytic construction of black hole magnetospheres. Higher order perturbative corrections are crucial in order...
In this work, we construct the Raychaudhuri equation in $f(\bar{R},\bar{T})$ gravity in the context of a non-canonical theory, which is the K-essence theory. We solved the modified Raychaudhuri equation for the additive form of $f(\bar{R},\bar{T})$, which is $f_{1}(\bar{R})+f_{2}(\bar{T})$. In this solution, we use two distinct scale factors to generate two kinds of $f(\bar{R},\bar{T})$...
Continuous gravitational wave (CW) searches targeted at known pulsars utilize electromagnetic observations of the sources to infer the phase-evolution parameters of the gravitational wave signal. We present a new method to perform Bayesian estimation of the amplitude parameters of a CW signal. The method leverages the well-established CW detection statistic, the F-statistic, and modern...
GEO 600 has been operating as a gravitational wave detector routinely since before the advanced detector era in mode known as "astrowatch". While exploring new technologies in large scale interferometry we keep the detector in an operational state allowing for calibrated data production. Technology highlights pioneered at GEO at high frequencies include the application of squeezing. That and...
Deep learning algorithms have excelled in various domains. Despite this success, few deep-learning models have seen full end-to-end deployment in gravitational-wave searches, both in real-time and on archival data. In particular, there is a lack of standardized software tools for quick implementation and development of novel AI ideas. We address this gap by developing the ML4GW and HERMES...
Crystal Eye represents an innovative space-based all-sky monitor designed to observe photons in the 30 keV to 50 MeV range. Utilizing a novel detection technique, this instrument features enhanced localization capabilities compared to current instruments, made possible by new materials and sensors. Its primary scientific objective is to detect electromagnetic signals from extreme phenomena in...
Quantum entanglement harvesting (EH) in the relativistic setup has recently attracted much attention. The formulation studies the possibility of two uncorrelated Unruh-DeWitt detectors getting entangled over time due to the effects of quantum vacuum fluctuations, depending on the motion and the background spacetimes. We investigate the effects of field temperature $T^{(f)}$ on EH between two...
Most of our knowledge about magnetars and pulsars is based on high-energy or radio observations. Due to the faintness of neutron stars in the infrared and the limited availability of space missions covering the wavelengths between millimeter wavelengths and the visible light, infrared studies of these compact objects are sparse. Yet, there is a lot of discovery potential at these wavelengths....
I will briefly summarize ongoing activities related to Strong Gravitational lensing, and illustrate a few very recent results of strong lensing events uncovered in the Euclid ERO data.
We present a series of numerical simulations of the pair creation process in the electrosphere of strange star using the Vlasov–Maxwell equations. The mechanism of pair creation in the electrosphere of compact objects is revisited, paying attention to evaporation of electrons and acceleration of electrons and positrons, which were previously not addressed in the literature.
The ANTARES neutrino telescope has collected data from February 2007 until its shutdown in February 2022. The full ANTARES dataset, including both track-like and shower-like events, has been used to search for both a diffuse, and a galactic neutrino flux. The latter being either evaluated agnostically through the contribution of the Galactic ridge with a single power law, or by evaluating...
Over 15 years after their discoveries, fast radio bursts (FRBs) still elude our understanding, despite the outstanding progress we have witnessed both observationally and theoretically. The huge luminosities of FRBs, and the apparent dichotomy between one-offs and repeaters, are just some of the theoretical challenges posed by such events. Among the countless proposed interpretations of FRBs,...
The orbital decay of binary pulsars is a very precise tool for testing general relativity and modified theories of gravity and for constraining the existence of additional neutron star charges. The orbital decay has been used for constraining scalar-tensor theories (STT) decades ago. In the present talk we demonstrate that the same simple methodology used for constraining STT can be applied to...
As a potential candidate for the late-time accelerating expansion of the Universe, the Chaplygin gas and its generalized models have significant implications to modern cosmology. In this study we explore the effects of dark energy on the internal structure of a neutron star composed of two phases, which leads us to wonder: Do stable neutron stars have a dark-energy core? To address this...
I will present an overview of temporal variability studies of Sgr A, discussing several observables, such as the flux distribution, the SED, the PSD and (higher order) structure functions, and will give an overview of how these are typically modelled in observational studies. A particular focus will be put on the temporal symmetry of Sgr A, which as a new and useful observable for the study...
Gamma-ray bursts (GRBs) are one of the most energetic explosions known in the Universe. Even though many GRBs have been observed since their discovery more than 50 years ago, and despite the success of the “fireball” model, there are still many open questions and unexplained observations. The origin of the plateau phase observed in the early X-ray light curve of GRBs (up to thousands of...
In 2006 we proposed the conjecture that rotating wormholes might be stable, while static ones might not be. In this talk we present an exact solution of the Einstein-Phantom Field equations similar to the Kerr solution. It is singular in a ring around the throat, but this singularity is geodesically complete and cannot be touched by null geodesics, our conclusion is that the singularity is not...
General Relativity has been extensively tested within the weak-field regime across various experiments. Recent years have seen significant progress in exploring the strong-field domain, now made possible through gravitational waves, X-ray data, and radio images of supermassive black holes like SgrA and M87. In this talk, I will discuss recent efforts to test General Relativity using black...
The landmark detection of a gravitational wave (GW) from the Binary Neutron Star Merger (BNS) GW170817 and its electromagnetic counterparts allowed us to study the Universe in a totally new way. Among the several discoveries made possible by GW170817, we can find the tightest constraints on the speed of gravity and the first measure of the Hubble constant (H0). Both these two measures were...
Gravitational lensing is the relativistic effect generated by massive bodies, which bend the space-time surrounding them. It is a deeply investigated topic in astrophysics and allows validating theoretical relativistic results and studying faint astrophysical objects that would not be visible otherwise. In recent years Machine Learning methods have been applied to support the analysis of the...
Supernova gravitational waves are the next candidates to those from the compact binary mergers. The gravitational waves generally depend on the supernova models, such as the progenitor mass and equation of state (EOS) for a higher-density region. So, even if one succeeds in detecting them in the future, it may be difficult to extract physical information from them. Up to now, the supernova...
We have investigated the evolutionary links between the isolated neutron star populations namely radio pulsars (RPs), anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), dim isolated neutron stars (XDINs), high-magnetic-field RPs (HBRPs), central compact objects (CCOs), rotating radio transients (RRATs), and long-period pulsars (LPPs) in the fallback disc model. The results of our...
There is no doubt that we live in a Gravitational Wave Background (GWB). In this talk we start from this hypothesis and show that if we take into account the energy generated by the GWB we have to extend Einstein's equations with a term $2\pi^2/\lambda^2$, where $\lambda$ is the Compton wave length of the graviton of the size of the observable universe. We call this model Compton Mass Dark...
In this talk the possible geodesic completeness of an electromagnetic dipole wormhole is studied in detail. The space-time contains a curvature singularity, and belongs to a class of solutions to the Einstein-Maxwell equations with a coupled scalar field that can be allowed to be phantom or dilatonic. Specifically, a numerical analysis is performed to examine congruences of null geodesics that...
In some modern theories, fields of the Standard Model of particle physics are allowed to interact with dark matter and dark energy. Such interactions, if they exist, may give rise to temporal evolution of the fine structure constant ($\alpha$) or its spatial variations. Consequently, stringent constraints on such theories can be placed by searching for any possible $\alpha$ variation. Recent...
I will present a review on the X-ray emission coming from the Galactic Center (GC), and in particular from the Central Molecular Zone, established from the results that have been obtained in the last 20 years with Chandra, XMM-Newton, INTEGRAL and other space observatories operating in the range 1-200 keV.
I will focus in particular on the emission that the GC super Massive Black Hole, Sgr...
ANTARES, an observatory for high-energy neutrinos located below the surface of the Mediterranean Sea, finished its observational mission in February 2022 after operating for 15 years. Positioned strategically in the Northern hemisphere and equipped with exceptional angular resolution, it was well-suited for its main goal: identifying the sources of cosmic neutrinos, particularly in surveying...
Causal discovery techniques have been introduced in the context of machine learning with the goal of finding and constraining causal relations between variables. Multiple algorithms for this task are available, amounting to different operational definitions of causal relations based directly on observational data. These tools have found wide application in disciplines that have limited access...
The search for continuous wave (CW) sources represents a new frontier of gravitational wave astronomy. The current and future LVK science runs may eventually reach the required sensitivities for the first detection of a rotating, distorted NS. At the same time, increasing efforts are being devoted to the search of long-transient signals (a few hours long) from newly born magnetars, a special...
Using a set of general-relativistic magnetohydrodynamics simulations that include proper neutrino transfer, we assess for the first time the role played by the fallback accretion onto the remnant from a binary neutron-star merger over a timescale of hundreds of seconds. In particular, we find that, independently of the equation of state, the properties of the binary, and the fate of the...
Gravitational waves (GWs) from compact binary coalescences are standard sirens that can probe the cosmic expansion history of the late-time Universe once the binary chirp mass-redshift degeneracy is broken. Methods for injecting redshift information into the inference process range from the direct detection of electromagnetic counterparts ("bright sirens") to the use of statistical properties...
Magnetars were discovered as soft gamma-ray repeaters by gamma-ray burst monitors. Their most energetic events are giant flares, seen as a bright, short flash followed by an exponentially-decaying periodic tail. There have been 3 such events seen in the Milky Way and Large Magellanic Cloud in ~60 years of observing. When these events occur in nearby galaxies their tail emission is...
The propagation of electromagnetic waves in vacuum is commonly modeled within the geometric optics approximation according to which light rays follow null geodesics. This is a sensible model whenever the wavelength is much smaller than the characteristic length scale of the medium through which it propagates since distinct wave phenomena such as diffraction are negligible in this case....
Forty years ago, Witten suggested that dark matter could be composed of macroscopic clusters of strange quark matter. This idea was very popular for several years, but it dropped out of fashion once lattice QCD calculations indicated that the confinement/deconfinement transition, at small baryonic chemical potential, is not first order, which seemed to be a crucial requirement in order to...
Current small scale cosmological controversies are coming down to the precision level of observations. The key point is whether a better understanding of baryonic physics, dark matter physics, or both is required to address these challenges. In this talk, I will describe how interferometric observations of strong gravitational lenses in the radio domain are uniquely contributing to address...
Ultraluminous X-ray sources are the X-ray binaries with X-ray luminosity exceeding the Eddington limit of a 10 solar mass black hole. Recent consensus is that these sources are powered mainly by super-Eddington accretion onto stellar-mass compact objects. An increasing number of discovered pulsating ULXs further advocate a possible scenario that neutron stars dominate a significant fraction of...
The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer (SMEX) satellite mission planned to fly in 2027. It has the participation of institutions in the US, Europe and Asia and aims at the construction of a gamma ray telescope for observations in the 0.2-5 MeV energy range. It will cover the full sky with a 120$\times$120 degrees$^{2}$ field of view, excellent energy resolution,...
The full proof of the nonlinear stability of Kerr consists of five papers, three written in collaboration with Jeremie Szeftel, one in collaboration with Elena and Jeremie Szeftel and another supporting paper authored by Dawei Shen. In my lecture I will describe the main architecture of the proof as well as some of the most important consequences.
Gamma-ray bursts observed in high energies allow the investigation of the emission processes of these still puzzling events. Here, we investigate the peculiar GRB 090510, a short GRB with an indication of plateau emission observed by the Fermi-LAT within the context of general relativistic magnetohydrodynamic code (HARM) to infer the jet opening angle, the energetics, the Lorentz Gamma factor,...
ZAIGA (the Zhaoshan long-baseline Atom Interferometer Gravitation Antenna) is a proposed underground long-baseline atom interferometer (AI) facility, aiming for experimental research on gravitation and related problems. It includes gravitational wave detection (ZAIGA-GW), dark matter detection (ZAIGA-DM), high-precision test of the equivalence principle of micro-particles (ZAIGA-EP),...
Follow-up observations are crucial to our understanding of fast radio bursts (FRBs), and have enabled studies of their host galaxies and persistent counterparts. As FRB localizations become routine, multi-wavelength simultaneous & post-burst observations will allow us to begin to constrain and characterise the progenitors and the emission mechanisms powering FRBs. In this talk, I will present...
Cosmic voids, large under-dense regions in the Universe, serve as promising laboratories for extracting cosmological information. They offer opportunities to explore deviations from $\Lambda CDM$ and provide insights into dark energy and modification of gravity. Upcoming surveys like Euclid will enable detailed void analyses, allowing access to a huge number of voids. Voids' significance lies...
The water Cherenkov neutrino telescope ANTARES was a 0.01 km3 volume
detector located in the Mediterranean Sea which aimed at the detection of high-energy cosmic neutrinos, specially those of Galactic origin. It operated from 2007 until the beginning of 2022, accumulating more than 15 years of data. Its advantageous location allowed ANTARES to explore the Southern Sky, including the Galactic...
In this talk, I will describe a theory for scalar QED near the black hole event horizon. In particular, I will show how to compute the electromagnetic eikonal S-matrix from elastic 2 → 2 scattering of charged particles exchanging soft photons in the black hole eikonal limit. The resulting ladder resummation agrees perfectly with the result from the first quantised formalism developed by ’t...
The standard sirens in the gravitational wave (GW) astronomy provide us with a direct measure of the cosmological distances independent of the cosmic distance ladder. When accompanied by an electromagnetic counterpart, it can also provide a redshift measurement, thus offering a new avenue to probe the cosmic expansion rate today, also known as the Hubble constant H0. However, the majority of...
Gamma-Ray Bursts (GRBs) are very energetic cosmological transients. Long GRBs are usually associated with Type Ib/c Supernovae (SNe), and we refer to them as GRB-SNe. Since the associated SN for a given GRB is observed only at low redshift, a possible selection effect exists when we consider intrinsically faint sources which cannot be observed at high redshift. Thus, it is important to explore...
In this talk we will present the first study of the spectrum of quasinormal modes of rotating Ellis-Bronnikov wormholes. We compute the spectrum using a spectral decomposition of the metric perturbations on a numerical background. We study the dependence of the modes on the angular momentum and show that rotation breaks the triple isospectrality of the symmetric and static wormhole.
We present a superfluid dark star model consisting of relativistic dark bosons with two-body self-interaction. The obtained masses, radii, and tidal deformability depend in a simple way on the boson mass and interaction strength. We report first results on binary mergers: the distinctive amplitude and frequency of the emitted gravitational waves are well within reach of terrestrial interferometers.
Numerous studies suggest that high-energy (HE) neutrinos and ultra-high-energy (UHE) cosmic rays could originate from extremely high-synchrotron peaked (EHSP) BL Lacs, which have been identified as effective particle accelerators. Due to the discovery of HE-neutrinos by the IceCube telescope, these hypotheses may shortly have the opportunity to be tested. In this work, we use a two-zone...
Multimessenger astrophysics provides unique and valuable insights into the properties and processes of the physical universe. The recent discovery of gravitational waves and high energy cosmic neutrinos, marked the beginning of a new era of the multimessenger astronomy. These new messengers, along with electromagnetic radiation and cosmic rays, give new insights into the most extreme...
Molecular clouds in the Galactic Center reprocess radiation from past outbursts, generating a strong Fe K$\alpha$ fluorescent line (6.4 keV). Reflecting the radiation that reaches them as mirrors, these clouds retain the historical activity of their illuminating sources. Studying this echo radiation provides crucial information about the source, the clouds' properties, and the relative...
New wide-field astronomical surveys are opening a new window on the Universe, by collecting data for extraordinarily vaste samples of galaxies. Strong gravitational lenses are rare astronomical events, whose actual number will increase of more than 100 times thanks to the unique data from the Euclid wide survey or the Rubin LSST observations. After finding such 100,000 strong lenses, they need...
For space gravitational wave (GW) detection, arm locking is a proposal useful in decreasing the frequency noise of the laser sources for current developing space missions LISA and Taiji/TianQin. In this talk, we discuss the application of arm locking to the Astrodynamical Middle-frequency Interferometric Gravitational Observatory (AMIGO) to decrease the frequency noise of laser sources. For...
Black hole solutions in General Relativity are parametrized by their mass, spin and charge. In this talk, I will motivate why the charge of black holes adds interesting dynamics to solutions of the Einstein equation thanks to the interaction between gravitational and electromagnetic radiation. Such radiations are solutions of a system of coupled wave equations with a symmetric structure which...
3XMM J185246.6+003317 is a transient magnetar located in the vicinity of the supernova remnant Kes\,79. So far, observations have only set upper limits to its surface magnetic field and spindown, and there is no estimate for its mass and radius. Using ray-tracing modelling and Bayesian inference for the analysis of several light curves spanning a period of around three weeks, we have found...
Exploring the mid-range $\gamma$-ray regime (0.1-50 MeV) remains a significant challenge in astrophysics due to the lack of sensitive instruments in this energy band. To address this gap, we propose the GammaTPC, a novel MeV $\gamma$-ray instrument concept utilizing a liquid argon (LAr) time projection chamber (TPC). This instrument aims to achieve an all-sky survey capability with a large...
A cosmological model with a new variant of Chaplygin gas obeying an equation of state(EoS), $p=-\frac{B}{ρ^α}$ where $B=B_0 a^n$[1], is investigated in the context of its thermodynamical behaviour. Here $B_0$ and $n$ are constants and $a$ is scale factor. We show that the equation of state of this ‘Variable Chaplygin gas’ (VGCG) can describe the current accelerated expansion of the...
We develop a model formalism to study the structure of a relativistic, viscous, optically thin, advective accretion flow around a rotating black hole in presence of radiative coolings. We use this model to examine the physical parameters of four black hole Ultra-luminous X-ray sources (BH-ULXs), namely mass ($M_{\rm BH}$), spin ($a_{\rm k}$) and accretion rate (${\dot m}$), respectively. While...
One of the most enigmatic challenges in contemporary time domain radio astronomy is understanding the nature of fast radio bursts (FRBs). These millisecond-duration, highly coherent radio flashes predominantly originate from beyond our Galaxy.
In this presentation, I will review the extensive efforts of the Italian research community in uncovering the origins and physical mechanisms behind...
The percent precision achieved on the values of the cosmological parameters defining the expansion rate and the geometry of the Universe has recently revealed some tension between the measurements of the value of the Hubble constant (H0) from local and early-Universe cosmological probes. The best strategy forward today is to develop independent and complementary techniques to measure H0, and...
The nature of dark matter is still a mystery. The possibility exists that dark matter is not made of elementary particles, but instead of “macroscopic” objects. In this class of scenarios, dubbed “macro DM”, the small interaction rates of dark matter are achieved through a small number density, as opposed to a small cross section. Examples of macro DM include clumps of strange quark matter...
It has been long known that the static Ellis-Bronnikov wormholes of GR are radially unstable. Here we study the radial perturbations of these wormholes in slow rotation up to second order. We find that rotation can potentially stabilize the unstable mode of the static wormholes.
The knowledge of what entered them is completely lost as black holes evaporate. This contradicts the unitarity principle of quantum mechanics and is referred to as the information loss paradox. Understanding the end stages of black hole evaporation is key to resolving this paradox. As a first step, we need to have exact models that can mimic 4-D black holes in General relativity in classical...
Neutrinos can be used to probe a vast number of physics phenomena, as in the case of searches for dark matter candidates in astrophysical objects. Dark matter particles can accumulate in massive astrophysical bodies and annihilate into Standard Model particles that can yield neutrinos. To detect neutrinos, large arrays of light sensors located at great depth and in a large volume of...
(pdf version attached)
Ever since the observation of GW170817 provided evidence for binary neutron star mergers as sources of gravitational waves and other transient emissions such as short gamma-ray
bursts, the development of electromagnetically informed gravitational-wave analysis pipelines
has gained relevance in the astrophysics community [2, 1, 3, 4]. In this talk, I will illustrate...
We collected the optical light curve data of 227 gamma-ray bursts (GRBs) observed with the TAROT, COATLI, and RATIR telescopes. These consist of 133 detections and 94 upper limits. We constructed average light curves in the observer and rest frames in both X-rays (from {\itshape Swift}/XRT) and in the optical. Our analysis focused on investigating the observational and intrinsic properties of...
We present a proof of concept for an alternative method of strong gravitational lens finding using a conditional Generative Adversarial Network (cGAN). We use Early Release Observation (ERO) images of the Perseus Cluster from Euclid, covering 0. 57sq.degrees on the sky, and the network is based on the pix2pix architecture with an adapted U-Net generator. We train our model to predict...
The International Virtual Observatory Alliance (IVOA) plays a crucial global role in establishing technical standards necessary for realizing the Virtual Observatory (VO). Our discussion focuses on the extensive adoption of the Multi-Order Coverage map (MOC) data structure for encoding the localization regions of gravitational wave sources detected by the LIGO, Virgo, and KAGRA (LVK)...
Neutron stars are one of the most suitable environments for probing physics under extreme states. For example, the quasi-periodic oscillations (QPOs) observed in a giant flare occurred in a strongly magnetized neutron star (magnetar), are carrying crucial information for extracting the neutron star properties. To theoretically explain the observed QPOs in GRB 200415A, we systematically examine...
The luminosity distance-redshift ($D_L$-$z$) relation of Type Ia supernovae (SNe Ia) yields evidence for a nonzero cosmological constant, i.e. `dark energy'. SNe Ia analyses typically involve fitting the $D_L$ and $z$ to the functional form derived theoretically from the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) metric. However, the metric in the epoch relevant to...
The large-scale structures such as Fermi Bubbles and eROSITA Bubbles provide a unique opportunity to study our Milky Way. However, the nature and origin of these large structures are still under debate. In this talk, I will present the identification of several kpc-scale magnetised structures based on their polarized radio emission and their gamma-ray counterparts, which can be interpreted as...
I will introduce a dynamical system formulation for inhomogeneous LRS-II spacetimes using the covariant 1+1+2 decomposition approach, that we recently proposed in 2404.01161. Our approach describes the LRS-II dynamics from the point of view of a comoving observer. Promoting the covariant radial derivatives of the covariant dynamical quantities to new dynamical variables and utilizing the...
In this paper, we develop a new model representing a spherically symmetric dark matter fluid sphere that could describe compact stellar objects. We consider that the compact star contains two regions namely, an isotropic inner core region with constant density and an anisotropic outer region with a specific realistic equation of state. We solve the system of field equation by assuming a...
Gravitational-wave astronomy has achieved remarkable progress over the
past decades, detecting waves across a wide range of frequencies.
However, the band around one Hz remains unexplored. This band is vital
for studying some of the most fascinating sources, including
intermediate-mass binary black hole mergers, early inspiralling compact
binaries, and possibly cosmic inflation. The...
This work explores the environmental influences on wormholes. Specifically, two classes of wormholes are considered: the Damour-Solodukhin and braneworld types. I will discuss the Damour-Solodukhin wormhole at the galactic center. Our results suggest that galactic Damour-Solodukhin wormholes are more stable than isolated ones under linear scalar perturbation. This enables the identification of...
Strong gravitational lensing by galaxy clusters is one of the most powerful tools to accurately probe the dark matter mass distribution in the densest regions of such structures, where multiple images are formed, and to test the currently accepted ɅCDM cosmological paradigm. Present and future observational facilities, such as the Euclid space telescope and the Vera Rubin observatory, are...
Based on: Phys. Rev. D 109, 023027 (2024), arXiv:2311.02169
Neutron stars (NSs) can have core densities several times that of the nuclear saturation density. One of the open questions in NS physics is the unknown high-density nuclear matter equation of state (EOS). By considering a number of proposed, phenomenological relativistic mean-field EOSs, we construct theoretical models of NSs....
Fast radio bursts (FRBs) are bright millisecond radio transients observed at extragalactic distances, whose origin is still highly debated. In this presentation, I summarize the key findings from two recent studies that leverage observations conducted with the Northern Cross radio telescope at 408 MHz, aimed at shedding light on the enigmatic FRB phenomenon. We investigated how prevalent...
Low angular momentum flows around black holes are likely to form standing shocks during the accretion processes. The shocks possibly encounter instabilities leading to various observational signatures associated with inflows and outflows. In our work, we address a range of issues like flaring in under-luminous Sgr A* with supermassive black hole and outflow properties in super-accretors like...
The GW-Universe Toolbox is a software package designed to simulate observations of various types of gravitational wave (GW) source populations using a wide range of GW detectors, including ground-based and space-based laser interferometers, as well as pulsar timing arrays. In its recent development, the GW-Universe Toolbox has been upgraded to enable the simulation of joint observations of...
Black holes are fascinating objects in nature. Although they are introduced as classical solutions in general relativity, their intrinsic nature should be quantum, which manifests during the black hole formation and evaporation processes. If string theory is claimed to be a quantum gravity candidate, it should be able to provide a consistent picture and elucidate some perspectives for black...
The observation of neutrinos of cosmic origin opens a whole new field for neutrino astrophysics. This quest has been paved by pioneering experiments in the second half of the 20th century and is now at the dawn of a new era thanks to numerous new proposals.
In this talk, I will review the continuation of neutrino astronomy following the ANTARES era by providing an overview of some of the...
We present a correlation observed in the afterglows of long duration Gamma-ray Bursts (GRBs) between the initial luminosity and average afterglow decay rate. We will show how this correlation, initially found at optical and X-ray wavelengths, is observed across the electromagnetic spectrum from the GeV to the radio. This correlation does not depend on the presence of specific light curve...
The Galactic centre region consists of the nuclear stellar disk (NSD), a flat, rotating stellar structure, and the nuclear star cluster (NSC), the densest concentration of stars in the Galaxy.
The NSC and NSD are distinct structures of the Milky Way, but also connected to the larger Milky Way structures, e.g. via the inflow and outflow of gas, and the infall of star clusters.
Our knowledge...
The search and characterization of the electromagnetic counterparts of gravitational wave emitters requires the collaborative efforts of researchers with both theoretical and observational expertise extending over the full range of the electromagnetic spectrum. The lessons learned from the first two observing runs of the advanced interferometers and the successful story of the detection of the...
In recent years, the precision of the Hubble constant ($H_0$) measurements has significantly improved, revealing some discrepancy between the estimates inferred from local and early-universe probes. This tension might be ascribed to the presence of unknown systematic effects or some deviation from the current cosmological model (flat $\Lambda$CDM), thus pointing to the need of new physics....
Fast Radio Bursts are known to exhibit scintillation and scattering phenomena , often attributed to the interaction of multiple screens. A common argument is that two screens, when appearing "pointlike" to each other, scintillate on both scales. This condition is commonly invoked to constrain scattering to FRB host galaxies. In this study, we explore this regime through simulations, revealing...
In the era of precision cosmology, where the accuracy of observational probes and the rigorous control of systematic uncertainties are of paramount importance, exploring the synergies among different methods can play a key role. Typically this is done on a global level and the results from different probes, coming from various datasets, are combined to increase the precision of the...
We review some recent advances in connection with the energy-momentum tensor and the semiclassical Einstein equations, symmetries and anomalies, effective actions, the renormalization group and other questions in the context of quantum field theory in curved spacetime.
Multimessenger signals from binary neutron star (BNS) mergers are promising tools to infer the largely unknown properties of nuclear matter at densities that are presently inac- cessible to laboratory experiments. The gravitational waves (GWs) emitted by BNS merger remnants, in particular, have the potential of setting tight constraints on the neutron- star equation of state (EOS) that would...
In Late 2014 India joined the International consortium for building and operating next generation mega ground based optical and infrared astronomy facility known as the “Thirty Meter telescope (TMT) International Observatory (TIO). India's in-kind contributions include Primary mirror Segment Support Assembly (SSA), Actuators, Edge Sensors, Primary mirror Segment Polishing, Observatory...
DECIGO (DECi-Hertz Gravitational-wave Observatory) and B-DECIGO are interferometric satellites expected to be launched in Japan around the 2030s targeting the observation of gravitational waves (GWs) from 0.1 Hz to 10 Hz. These missions will unveil populations of intermediate-mass black hole mergers, provide frequent opportunities to localize the host galaxy of a binary neutron star before its...
TianQin is a Chinese space-borne gravitational wave detector proposed in 2014, and aims to detect gravitational waves in the frequency range of 1mHz ~ 1 Hz, with three earth orbiting satellites with an orbital radius of about 105 km forming an equilateral triangle with side length 1.7×105 km. The free falling test masses are used as inertial references to provide measurement points for...
The integration of Artificial Intelligence (AI) into astronomy and astrophysics marks a transformative era in the exploration of the Universe, enhancing the analysis of vast data sets with unparalleled efficiency and precision. AI is revolutionizing the usability of observational data, expanding our understanding of various cosmic phenomena. Blazar research particularly benefits from the...
The interface between Quantum Information and Quantum Field Theory --especially Quantum Gravity -- is emerging as a forefront area of fundamental physics. But there is some tension between the way the basic concepts are commonly understood by the two communities. In particular, are the `Coulombic modes' of the gravitational field sourced by quantum matter quantum mechanical? They are not...
Pulsar timing arrays are sensitive to low-frequency gravitational waves with periods of months to decades. They do so by precisely timing a collection of millisecond pulsars, whose extremely stable rotation makes them ideal for measuring perturbations in spacetime. Gravitational waves induce correlations in the pulse arrival times that follows a characteristic pattern known as the...
After the first groundbreaking observation of gravitational waves emitted by the collision of two black holes on 14 September 2015, the LIGO-Virgo-KAGRA network has completed three successful observing runs yielding nearly a hundred events. All detections were compatible with short transients emitted by the coalescence of compact binaries composed of black holes and/or neutron stars. The first...
In the field of gravitational wave (GW) detection, groundbreaking discoveries like those made by the LIGO, Virgo, and KAGRA collaborations signify the culmination of extensive interdisciplinary efforts spanning various research fields. These detectors grapple with numerous noise sources that undermine their sensitivity. To surmount these challenges, we are exploring strategies that harness...
To precisely model or solve the binary problem in general relativity is a formidable challenge for both astronomy and gravitational physics. We will provide an exact one-body approach for the conservative part of such a problem, which applies to the whole three stages of the binary merger process. It utilizes a rotating gravitational field comprising two joined patches as the background for...
The Comic Microwave Background is one of the most powerful cosmological observables, allowing to probe a variety of phenomena, from the Early Universe and high energy physics at scales never achievable in earth facilities, to the evolution of the Universe at much recent epochs. In this talk I will provide an overview of signatures of new fundamental physics, for which the CMB can play the...
Gravitational waves (GWs) from the coalescence of compact binaries are among the most promising cosmological probes. Their signal can be used to study the late-time cosmic expansion of the Universe independently from other known cosmological probes and without the need for an intermediate calibrator. However, this is only possible if the binary redshift is known.
Different methods have been...
Geometric optics limit is considered to be a good-enough approximation for the calculation of distances and image distortions in curved spacetime. It is usually assumed that spherical waves are emitted from a point source and we observe a section of the wavefront. In the geometric optics limit, this section is represented by a thin bundle of rays. Accordingly, the intensity profile on the...
The Bopp-Podolsky theory is a gauge-invariant and Lorentz-invariant theory of electromagnetism that introduces a new hypothetical constant of Nature with the dimension of a length, called the Bopp length. The theory was introduced by Bopp in 1940, and independently by Podolsky in 1942, in order to cure the infinite field energies of point charges. If one sets the Bopp length equal to zero one...
Cosmological models and their parameters are widely debated, especially about whether the current discrepancy between the values of the Hubble constant, H 0, obtained by Type Ia supernovae (SNe Ia) and the Planck data from the cosmic microwave background radiation could be alleviated when alternative cosmological models are considered. Thus, combining high-redshift probes, such as gamma-ray...
The era of Gravitational Wave (GW) Astronomy started on 2015, with the first observation of GWs from the merger of a binary black hole (BBH) system by Advanced LIGO. Two years later, the detection of GWs from a binary neutron star (NS-NS) merger by the Advanced LIGO and Advanced Virgo network and of the associated electromagnetic (EM) signals marked the birth of multi-messenger astronomy with...
In this talk, I will describe the results of the most extensive multiwavelength observational campaign ever carried out on the prototype of the class of transitional millisecond pulsars, PSR J1023+0038. The campaign aimed to find an explanation once and for all for the peculiar variability pattern shown by the source during its current active X-ray state. The results of the data analysis...
Although General Relativity predicts the presence of a singularity inside of a Black Hole, it is not a complete theory of gravity. A real structure of a Black Hole interior near an expected singularity depends on the UV completion of gravity. In this paper, we establish that the question whether singular spherically symmetric solutions are absent is governed by the functional form of a...
Gamma-ray Bursts (GRBs) are one of the most energetic phenomena in the cosmos, whose study probes physics beyond the reach of laboratories on Earth. Yet, our quest to fully unravel the origin of these events and comprehend their underlying physics is far from complete. Central to this pursuit is the rapid classification of GRBs to guide follow-up observations and analysis across the...
We present the spectrum of quasinormal modes of rapidly rotating black holes. We apply a spectral decomposition on the perturbations of the metric and other dynamical fields. We compare our results with the modes computed using other methods, study the accuracy of our calculations, and investigate the application of our method to black holes in alternative theories of gravity.
I will give an overview of recent work in causal set theory and the status of the field.
G4S_2.0 (Galileo for Science) is an ongoing project funded by the Italian Space Agency (ASI) and carried out by the Center for Space Geodesy (ASI-CGS) in Matera, the Istituto di Astrofisica e Planetologia Spaziali (IAPS/INAF) in Rome, and the Politecnico di Torino (POLITO). The project's goal is to address several intriguing challenges, including Fundamental Physics measurements using the...
The Galactic Center provides a unique opportunity to observe galactic cores, objects in the close proximity to a supermassive black hole (SMBH), and star formation channels that exhibit imprints of this peculiar environment. This habitat hosts, in addition to the SMBH Sgr A * , a surprisingly young cluster with the so-called S-stars. These stars orbit the SMBH on timescales of a few years with...
In this work we analyze traversable wormhole spacetimes in the framework of a covariant generalization of Einstein's General Relativity known as energy-momentum squared gravity. Here, we show that a wide variety of wormhole solutions for which the matter fields satisfy all the energy conditions, namely the null, weak, strong and dominant energy conditions, exist in this framework, without the...
The launch of the IXPE telescope in late 2021 finally made polarization measurements in the 2-8 keV band a reality, more than 40 years after the pioneering observations of the OSO-8 satellite. In the first two years of operations, IXPE targeted more than 60 sources, including four magnetars, neutron stars with magnetic fields in the petaGauss range. In this presentation I will summarize the...
Constraining cosmological parameters for galaxy clustering analyses using the three-point correlation function, despite being pivotal, has historically been limited by the high computational cost of modelling. Here, we introduce a new emulator, based on a convolutional neural network, developed within the framework of a Euclid Preparation Key-Project activity, which substantially accelerates...
We consider the torsional completion of the theory of gravity in which torsion is a propagating axial-vector field: we show how this changes the energy conditions leading to the singularity formation being avoided. We discuss how the same construction possesses regular matter distributions even in the case of a single particle. We give a brief discussion also about the localization of such...
I will discuss the detection of exotic compact objects, such as primordial black holes, boson stars, etc, with gravitational waves from a binary system where the mass ratio is extremely small (or large), and show that such exteme mass ratio inspirals and mini-EMRIs are ideal systems for detection of very light exotic compact objects, and that they serve as important targets for space-based and...
One of the primary research aims of the Laser Interferometer Space Antenna (LISA) mission is to comprehensively map the Kerr spacetime, a fundamental pursuit in the realm of general relativity. To achieve this goal, it is essential to develop precise tools capable of discerning any deviations from the Kerr geometry. Extreme mass-ratio inspirals (EMRIs) stand out as particularly promising...
In this contribution a new metric with seven parameters is found.
The metric possess the following features: mass, rotation, charge,
magnetic dipole, massive quadrupole, octupole, and hexadecapole.
These spacetime is versatile and realistic for representing compact objects like neutron stars. It has several astrophysical applications, for
example to study the chaotic behavior of geodesics...
In this talk, I revisited the model of a dust-enshrouded star orbiting a low-luminosity galactic nucleus (Zajacek et al., 2014, 2016, 2017). Although it is quite challenging for dust to survive in hot X-ray-emitting plasma surrounding supermassive black holes (SMBHs), now we have an observational evidence that compact dusty objects or G objects can approach the SMBH in the Galactic center (Sgr...
The fourth observing run (O4) of LIGO-Virgo-KAGRA is now ongoing, relying on the most sensitive network of gravitational-wave interferometers to date. In this talk, I will highlight in a multi-messenger context some of the most recent astrophysical findings and their implications for massive-star evolution, supernova theory, compact binary populations, and the search of electromagnetic and...
We study the effects that a $\sqrt{-F_{\mu \nu}F^{\mu \nu}}$ in the action can have and we find,
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Combined with a Maxwell term $-F_{\mu \nu}F^{\mu \nu}$ it gives a confining behavior.
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adding a ¨mass term¨$A_{\mu}A^{\mu}$, a source genrates a Coulomb component with asymptotic strength independent of the charge at the source, the gauge fields produce a cloud of charge, so as to get...
The detection of dark matter is a challenging problem in modern physics.
We provide a proposal to detect the coupling of ultralight scalar dark matter to quarks and gluons as well as the coupling of ultralight axion dark matter to gluons with long-baseline atom interferometers. The ultralight scalar and axion dark matter could induce the oscillation of the nuclear charge radii and then...
By studying quantum fields on classical curved spacetimes, Gibbons and Hawking managed to derive the thermodynamical properties of black holes, while making at the same time the first robust prediction of a semiclassical theory of gravity. Nevertheless, they quickly realized that black hole evaporation leads to sudden bursts of energy and loss of information. It can be argued that these...
Constraining the expansion history of the Universe with new and complementary approaches is crucial now that we are in the age of precision cosmology, where managing systematic effects and increasing the accuracy of the measurements is essential.
In this talk, I will present how the ages of the oldest objects in our Universe can shed light on its expansion history, both in the local...
Ultraluminous X-ray sources (ULXs) have captivated researchers for decades due to their exceptionally high luminosities and unique spectral characteristics. Some of these sources defy expectations by exhibiting super-Eddington luminosities with respect to stellar mass sources even in their low-hard state. Numerical steady-state calculations suggest that ULXs in this state can be explained as...
We introduce a new approach to measuring proper distances between space-like separated events in Minkowski spacetimes of any dimension. Interestingly, this approach allows us to measure distances up to the Planck scale with arbitrary precision. It also enables us to define reference frames and evaluate some kinematic quantities along time-like paths.
The magnetic field of a neutron star plays a key role in its evolution and the dynamics of the emission, both electromagnetic and gravitational. Nevertheless the field configuration of these stars is still highly uncertain. In this talk I will review the main issues involved in modelling the magnetic field, and recent advances.
Upcoming experiments of the Cosmic Microwave Background (CMB) will reach unprecedented sensitivity to polarization, thus allowing to target the first detection of primordial CMB B-modes and possibly shed new light on reionization history, cosmic birefringence, neutrino masses, and large-scale CMB anomalies. However, accurate measurements of the CMB polarization require exquisite control of...
Low-redshift observations play a crucial role in constraining cosmological parameters but current data on baryon acoustic oscillations and Supernovae of Type Ia (SNIa) cover up to $z\sim2.5$. Gamma-Ray Bursts (GRBs) stand out as one of the most promising observables as they exhibit characteristics that suggest they are potentially standardizable candles. This allows their use to extend the...
The purpose of this work is to study the orbital evolution under the combined effect of disk-drag and GW-emission for E/IMRIs endowed with accretion disk. We study the dependence of disk-torque and GW-torque on the orbital parameters of compact companions. We employ a semi-relativistic technique to study E/IMRI dynamics evolving under most general elliptical-orbits in the equatorial plane and...
We evaluate the surface energy~(${\cal E}_{s}^{\pm}$), rotational energy~(${\cal E}_{r}^{\pm}$) and electromagnetic energy~(${\cal E}_{em}^{\pm}$) for a Kerr-Sen black hole~(BH) having the event horizon~(${\cal H}^{+}$) and the Cauchy horizon~(${\cal H}^{-}$).
Interestingly, we find that the sum of these three energies is equal to the mass parameter i.e. ${\cal E}_{s}^{\pm}+{\cal...
We find that a field with oscillations of matter in proper time has the properties of a zero-spin bosonic field. A particle observed in this field is a proper time oscillator. Neglecting all quantum effects, a proper time oscillator can mimic a point mass at rest in general relativity. The spacetime outside a 'stationary' proper time oscillator is a Schwarzschild field.
Gravitational-wave detections and open public alerts enabled prompt multimessenger studies for the global community. There is an ongoing effort to assimilate and invent machine learning techniques that will allow faster and more confident detections. Better characterized detections of more gravitational-wave events thereby will expand multimessenger science. I will highlight trailblazing...
We calculate the effect of dark matter on the ringdown waveform and shadow of supermassive black holes at the core of galaxies. Our main focus is on the supermassive black hole at the core of M87, which is large enough to allow for viable observational data. We compare the effects of a dark matter spike to those expected from a galactic halo of the same mass. Our calculation for the halo...
Next-generation gravitational-wave detectors will be able to explore a broad range of science case studies. Evaluating their detection and parameter-estimation capabilities is a mandatory step in the planning process. We will start by discussing currently available data analysis tools that allow us to do forecasts. In particular, we will talk about GWFish, a software that simulates...
Prior studies have revealed the presence of young massive stars in the central 0.5 pc of the Galactic Centre, prompting questions about their properties and formation in the immediate vicinity of the massive black hole Sagittarius A*. Intriguingly, the shape of the initial mass function (IMF) in this region appears to deviate from the standard Salpeter/Kroupa law. However, our knowledge of the...
The $\Lambda$-ColdDarkMatter model, despite being in well agreement with many observational datasets at the background level, exhibits a growth of perturbations troubled by some inconsistencies: the $H_0$ and $\sigma_8$ tensions. Adopting a theoretical perspective, this opens the question about the possibility of having a cosmological model, based on other than a cosmological constant and...
An optically thin advective accretion disk appears to be indispensable in explaining the hard spectral state of black hole sources. We explore, with the help of general relativistic magnetohydrodynamic (GRMHD) simulations, how a large scale stronger magnetic field helps in transporting angular momentum in disk and outflow/jet, depending on the field geometry and plasma-β parameter, basically...
We construct the canonical ensemble of a matter thin shell in
asymptotically AdS using the Euclidean path integral approach.
We impose spherical symmetry, the Hamiltonian and momentum constraints,
the hot AdS regularity conditions and the asymptotic behaviour of AdS
on the metrics summed in the path integral and obtain the reduced action,
which can be regarded as a generalized free...
Since the first theoretical proposition of a black hole solution, it has been one of the most investigated questions that what would be the appearance of a black hole. There have been hundreds of black hole solutions in various frameworks for which studies are available dealing with the optical images of these black hole models. Currently, we call it the black hole shadow as it turns out due...
Abstract. Since the work of Kaluza it has been known that Maxwell's equations are mathematically a subset of the Ricci curvature tensor in five dimensions. In the present paper a complete set of equations for the 5D Ricci curvature tensor is described that reproduces both the 4D Einstein gravitational equations and the equations of electromagnetism. The fifth row and column of 5x5 matrices...
Causal sets are locally finite, partially ordered sets (posets), which are considered as discrete models of spacetime. On the one hand, causal sets corresponding to a spacetime manifold are commonly generated with a random process called sprinkling. This process keeps only a discrete set of points of the manifold and their causal relations (loosing the spacetime symmetries in each...
Identifying gamma-rays and rejecting the background of cosmic ray hadrons are crucial for very-high-energy gamma-ray observation and relevant scientific research. Based on the simulated data from the square kilometer array (KM2A) of LHAASO, eight high-level features are extracted for the gamma/hadron classification. Machine-learning (ML) models, including logistic regression, support vector...
In this work we study, within the framework of Cowling approximation, the effect of the electric charge on the gravitational wave frequency of fluid oscillation modes of strange quark stars. For this purpose, the dense matter of the stellar fluid is described by the MIT bag model equation of state (EoS), while for the electric charge profile, we consider that the electric charge density is...
Superluminous supernovae are a class of exceedingly bright transients whose luminosity cannot be comfortably explained by the standard 56Ni-decay picture. The quest for an alternative scenario has pointed at the contribution of a nascent millisecond magnetar and/or at the interaction of the supernova ejecta with a circumstellar medium surrounding the progenitor star; however, some of the...
Regular black holes have become a popular alternative to the singular mathematical black holes predicted by general relativity as they circumvent mathematical pathologies associated with the singularity while preserving crucial black hole features such as the trapping of light. Based on the assumption that semiclassical gravity is valid in the vicinity of their apparent horizons, we examine...
It is a well-known fact that light rays do not follow the null geodesics of spacetime, instead, they propagates along the null geodesics of the effective spacetime. In my presentation, we discuss the construction of the effective spacetime by studying the electromagnetic perturbations of black holes in general relativity coupled with nonlinear electrodynamics. Additionally, we explore the...
We present the largest optical photometry compilation of Gamma-Ray Bursts (GRBs) with measured redshifts ($z$). Our dataset includes 64813 observations of 535 events (including upper limits) from 28 February 1997 to 18 August 2023. We introduce grbLC, a user-friendly web tool for visualising photometry, coordinates, redshift, host-galaxy extinction, and spectral indices for each event in our...
The cosmological constant problem enfolds one of the most long-standing issues in physics: the incompatibility between Quantum Field Theory and General Relativity. Within this background, the Archimedes experiment aims to investigate the relationship between zero-point quantum fluctuations of the electromagnetic field and gravity. Using a highly sensitive suitably designed beam-balance,...
GRB jets are launched from rapidly spinning black holes (BHs), anchored by a strong magnetic field, a process known as the Blandford–Znajek (BZ) mechanism. However, most BHs from core collapse are likely born slowly spinning, raising the question of what type of transients emerge in those cases. With the upcoming launch of LSST, it is imperative to map the wide spectrum of transients from...
I will present a recently funded Open Science ERC AdG program that aims to implement a single massively parallel end-to-end framework called "Commander4" for the joint analysis of past, present and future CMB experiments. This framework will build on the existing Commander code that was used by Planck for component separation, and subsequently generalized by the BeyondPlanck and Cosmoglobe...
Dark Gravity is a natural extension of general relativity
in presence of a flat non dynamical background. Matter and radiation
fields from its dark sector, as soon as their gravity dominates over our side fields gravity, produce a constant acceleration law of the scale factor. After a brief reminder of the Dark Gravity theory foundations the confrontation with the main cosmological probes is...
This work investigates the long-term evolution of two bodies in nearby initially coplanar orbits around a central dominant body, perturbed by a fourth body on a distant Keplerian orbit. Previous works on this setup enforced circular orbits by adding a spherical potential of extended mass. This results in a long-term coherent evolution with nearly coplanar orbits experiencing only small...
In this talk we present the analysis of a large class of extended mimetic gravity Lagrangians, which allow the embedding of the Lemaître-Tolman-Bondi (LTB) models in spherically symmetric spacetimes. Using the LTB embedding, we are able to completely decouple the dynamics along the radial direction and obtain exact solutions of the modified Friedmann equations. Moreover, we introduce a...
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...
Two broad sets of classes of gravitational field propulsion techniques are investigated: classical general relativity field propulsion, and the quantum manipulation of spacetime. Classical approaches in this paper include a Forward Coil, which concentrates an acceleration field in the center of the coil, the use of wormholes, and a tokamak plasma quadrupole oscillator, creating gravitational...
We present theoretical estimations of the event rates for the interaction between a right-handed neutrino dark matter with an electron bound to a Xenon atom. Motivated by recent results on dark matter in cosmological and astrophysical contexts, we study a fermionic dark matter candidate with a mass of 200 keV as a case of example. The interaction occurs through an effective electromagnetic...
Quasar absorption line is a powerful tool for studying the universe, enabling us to probe distant gas, dust, and galaxy formation and evolution. However, detecting Ca II absorbers is particularly challenging, requiring significant time and effort. Existing deep learning methods often produce a high number of false positives and still require extensive manual verification, achieving an...
In our presentation, we demonstrate the spacetime properties of a monopole within nonlinear $\sigma$-models in Eddington inspired Born-Infeld gravity. Specifically, we investigate characteristic circular orbits of test particles and photons, including circular null geodesics, marginally bound orbits, and stable circular orbits, as influenced by spacetime parameters. Additionally, we discuss...
The Einstein Telescope (ET), third generation gravitational wave (GW) interferometer, will explore a large volume of the universe, detecting up to 10$^{5}$ binary neutron star system mergers (BNS) per year, beyond redshift z ~ 3. This will clearly revolutionize GW multi-messenger (MM) astrophysics. A significant amount of electromagnetic (EM) counterpart candidates will be provided by...
The huge luminosity, the redshift distribution extending at least up to z∼10 and the association with the explosive death of very massive stars make long GRBs (i.e., those lasting up to a few minutes) potentially extremely powerful probes for shedding light on main open issues in our understanding of the early Universe: star formation rate evolution up to the first generation of stars...
An alternative formulation of classical electromagnetism relying on torsion in metrically flat spacetime in four dimensions is presented. Unification with gravitation is then obtained as a direct consequence of the extension to the more general case of metrically curved spacetime. A propagating equation for the electromagnetic potential is derived and discussed. In the same context, it is also...
We shall discuss a system consisting of three extremally charged black holes moving in their own gravitational and electromagnetic fields. Based on a method by Ferrell & Eardley for an arbitrary number of holes, we take the exact static Majumdar-Papapetrou spacetime, and perturb it by giving the holes small velocities.
Suprisingly, the complicated equations can be reduced to a classical...
We study the linear polarization from the accretion disk around horizonless compact objects. Previous works have shown that these spacetimes can have significantly different lensing properties from black holes. In particular, their relativistic images can exibit a qualitatively new ring structure, inside what would be the shadow region. We search for characteristic signatures which could...
Causal set theory offers a simple and elegant picture of discrete physics. Unfortunately, though, the vast majority of causal sets do not look anything like continuum spacetimes, and must be excluded if the theory is to describe our actual universe. I will summarize recent results that show that almost all non-manifoldlike causal sets are, in fact, extremely strongly suppressed in the...
In this talk I will present cosmological results from the recent work carried on by the BeyondPlanck collaboration: a Bayesian end-to-end analysis of Planck LFI raw data. This novel approach allowed to seamlessly go through all the steps of a classical CMB analysis pipeline in an integrated framework: commander3. Cosmological results we produced are therefore naturally marginalized over all...
The discovery of a cold (~10,000 K) disc-like structure around the super-massive black hole at the centre of the Milk Way, Sagittarius A (Sgr A), has challenged our understanding of the gas dynamics and thermodynamic state of the plasma in its immediate vicinity. State-of-the-art simulations do not agree whether or not such a disc can indeed be a product of the multiple stellar wind...
The aim of this analysis of a historical compilation of Hubble-Lemaître constant (H0) values in the standard cosmological model is to determine whether or not the stated error bars truly represent the dispersion of values given. For this analysis, a chi-squared test was executed on a compiled list of past measurements. It was found through statistical analyses of the data (163 data points...
A thin circular structure vibrating in the central plane of a black hole will be investigated. This circular ring (string loop) can be considered a simplified model for thin magnetic flux tubes (in plasma physics), and connections to accreting fluid structures around the black hole will be demonstrated. The stability of the string loop and the frequencies of its vibrational modes will be...
The NICER (Neutron star Interior Composition ExploreR) X-ray telescope on the International Space Station can provide a powerful approach to the magnetar and FRB connections using its large effective area and prompt follow-up observation of transients. Our NICER magnetar and magnetosphere (M&M) science collaboration has observed several transient magnetars and FRB-related phenomena. We...
We present a detailed analysis of the static spherically symmetric solutions of a sixth-derivative gravity model with complex conjugate poles ( Lee-Wick gravity ) in the effective delta source approximation. The solutions exhibit an interesting structure that depends on the real and imaginary part of the Lee-Wick mass $\mu=a +i b$. In particular, because of the oscillating behavior of the...
We use the numerical continued fraction method to investigate quasinormal mode spectra of extremal and non-extremal Reissner-Nordström black holes in the low and intermediate damping regions. In the extremal case, we develop techniques that significantly expand the calculated spectrum from what had previously appeared in the literature. This allows us to determine the asymptotic behavior of...
I will discuss the use of machine learning and more specifically of convolutional neural network (CNN) to enable fitting of blazar (or other objects) SEDs with numerically costly models. In particular, I will describe the necessary ingredients, the numerical approach and tools, the setup of the neural network and the training steps. Finally, I will discuss future plans and improvements.
The gravitational quantum field theory is a gauge formulation of the gravity dynamics based on the inhomogeneous spin gauge symmetry, which leads to the generalized Einstein equation. In order to test this theory, we linearize the dynamic equations of gravitational interaction by keeping terms up to the leading order in the dual gravigauge field. We then apply the linearized dynamic equations...
The paleo-detector technique proposes to use long-age minerals, which have been exposed to an enormous flux of particles, as astroparticle detectors. Some of these particles should have interacted with mineral nuclei, generating linear defects in the crystalline structure in the form of tracks. The paleo-detectors have been proposed to detect dark matter and neutrinos, using minerals found...
Cosmic Microwave Background (CMB) observations traditionally assume an isotropic and homogeneous infinite Universe. However, a growing number of large-scale anomalies and dipoles in the literature suggest the need to revisit these assumptions. A physically well-motivated explanation for these anomalies is the impact of the Universe's topology. Even in a flat Universe, the topology can...
We propose a theory to explain the mechanism that stabilizes an electron. We show that the intrinsic divergences that occur in quantum electrodynamics can be removed by casting it within general relativity. The infinities are compensated by the curvature created by the intense energy density of the electromagnetic field in the vicinity of the electron. Using the concept of hydrostatic...
The innermost regions of most galaxies are characterised by the presence of extremely dense nuclear star clusters, which sometimes appear alongside larger stellar structures known as nuclear stellar discs. Understanding the relationship between nuclear star clusters and nuclear stellar discs is challenging due to the large distances to other galaxies, which limits their analysis to integrated...
The detection of the gravitational wave (GW) signal GW170817 and the electromagnetic (EM) signal AT2017gfo confirmed the association between binary neutron star (BNS) mergers and kilonovae (KNe) and showed the potential of joint detection to unveil the nature of neutron stars and the nucleosynthesis of heavy elements in the Universe. The next-generation GW interferometers, such as the Einstein...
We study the shadows cast by rotating hairy black holes with two non-trivial time-periodic scalar fields having a non-flat Gaussian curvature of the target space spanned by the scalar fields. Such black holes are a viable alternative to the Kerr black hole, having a much more complicated geodesic structure and resulting shadows. We investigate how a nontrivial Gauss curvature alters the...
I will illustrate a new method to search for long transient gravitational wave signals, like those expected from fast spinning newborn magnetars, in interferometric detector data.
Because of the fast frequency variation of these signals, matched filter techniques used for standard semi-periodic persistent signals are computationally unfeasible.
We explored a different approach by means of...
The electromagnetic field of a particle moving in the vicinity of a Schwarzschild black hole is calculated. The energy emitted by the particle is calculated using the multipole expansion approach. The particle is considered as it approaches the event horizon of the black hole. The electromagnetic field of this particle is calculated in the limit of the event horizon approach. It is shown that...
One of the best known interactions between quantum field theory and general relativity is the way that horizons gain an associated entropy, given by an area law. Entanglement entropy is a particularly promising candidate as the source of this entropy, and providing an explanation for black hole entropy as entanglement entropy was one of the initial motivations behind the formulation of causal...
We study asymptotic symmetries for 3d Chern-Simons theory as a gauge theory of so(3,2), sl_4 and sl_5 algebras. For the near horizon boundary conditions we present solutions from several projectors from Chern-Simons to the metric formulation. These solutions are generalized BTZ solutions for our theories. We also study the classification according to so(3,2) one parameter subgroups and...
Despite decades of research, cosmology still lacks reliable probes to study the Universe in the intermediate redshift regime (from $ z = 1 $ up to $ z = 1100 $). Very few astronomical objects observed at such high distances can be standardized. We present the case of Gamma-Ray Bursts (GRBs, $ z < 9.4 $). For these sources, the observational luminosity distance can be derived using an empirical...
We investigate the shadows produced by naked singularity spacetimes. Most analytical solutions for black hole shadows have focused on scenarios where the geodesic equations for photons. We examine the spherical null naked singularity metric, which is a spherically symmetric solution to Einstein's equations. Additionally, we consider a static, axially symmetric singular solution of the vacuum...
The search for gravitational wave signals in the data collected by the current ground-based interferometers is a complex problem, especially when only one detector operates. Modern deep learning approaches could contribute to find a solution. I'll discuss the detection problem and present the work detailed in https://iopscience.iop.org/article/10.1088/1361-6382/ad40f0 where we investigate the...
We discuss a possible electromagnetic analog of MOND by extending the recently proposed mechanism of emergence of MOND from quantum fluctuations of spin connection in precanonically quantized general relativity (arXiv:2311.05525 [gr-qc]) to a classical particle in the hybrid electric field that consists of a classical external field and quantum vacuum fluctuations over it. The dispersion of...
Using ancient minerals as paleo-detectors is a proposed experimental technique expected to transform supernova neutrino and dark matter detection. In this technique, minerals are processed and closely analyzed for nanometer scale damage track remnants from nuclear recoils caused by supernova neutrinos and possibly dark matter. These damage tracks present the opportunity to directly detect and...
There is an open debate about whether some galactic centers (including Sgr A*) could actually be supermassive dark matter cores made of fermions with masses in the range of 60-350 keV. We discuss the possibility of pinpointing mergers of such cores using mHz gravitational waves with the forthcoming space-based interferometers and assess the consequences of the possible outcomes from the...
The no-hair conjecture asserts that all black holes in general relativity (GR) coupled to any matter must be Kerr–Newman type. The three independent externally observable classical parameters— mass, electric charge, and angular momentum — uniquely determine all the information about the matter that formed into a black hole. However, the conjecture fails in some cases where the matter sources...
The exceptionally low mass $0.77_{-0.17}^{+0.2} M_{\odot}$ inferred of the central compact object (CCO) XMMU J173203.3--344518 within the SNR HESS J1731--347, of age $\approx 4.5$ kyr, challenges the standard core-collapse scenario of NS formation. The observed (likely post-AGB) star of $\approx 0.6 M_\odot$, at $0.3$ pc from XMMU J1732, also within the SNR, enriches the scenario. To address...
The large-scale $B$-mode polarization of the Cosmic Microwave Background (CMB) holds immense potential for revealing high-energy physics from the early Universe. Detecting this signature would likely indicate the emission of primordial gravitational waves following the Big Bang, providing crucial insights into the physics that created them. However, observing this faint signal is extremely...
In this work, we investigate the global structure of shock-induced general relativistic magneto-hydrodynamic (GRMHD) accretion flows around a Kerr black hole, where the disk is threaded by the radial ($b^r$) and the toroidal ($b^\phi$) magnetic fields. In doing so, we consider an advective, axisymmetric, and optically thin accretion flow that is confined in the disk mid-plane. In addition, we...
We present phenomenological analysis of photon lensing in an external gravitational background in the case of photons and neutrinos, and propose a method to incorporate radiative effects in the classical lens equations. The study is performed for a Schwarzschild metric, generated by a point-like source, and expanded in the Newtonian potential at first order. We use a semiclassical approach,...
Our Galactic Center (GC) is the closest and most accessible galactic nucleus, which provides us with the unique opportunity to conduct resolved star formation studies in extreme environments. Despite the need for very high gas densities to overcome the tidal field of the supermassive black hole Sgr A*, and induce gravitational collapse, there is evidence for star formation taking place at the...
Unmodeled gravitational-wave signals from magnetars are expected to be weak and challenging to detect in LIGO-Virgo-KAGRA data. We introduce a new method to denoise and stack signals from repetitive magnetar bursts, such as the 2020 SGR 1935+2154 burst storm which produced 217 bursts in 1120 seconds. Our method involves identifying bursts in electromagnetic data and searching for corresponding...
We define an entropy product function (EPF) for Taub-Newman-Unti-Tamburino(TNUT) black hole(BH) following the prescription suggested by Wu et al. [PRD 100, 101501(R) (2019)].
The prescription argues that a generic four-dimensional TNUT spacetime might be expressed in terms of three or four different types of thermodynamic hairs. They can be defined as the Komar mass($M=m$), the angular...
With Dark Matter still eluding detection a window has opened for new ideas in the field. One such idea is to utilize the advent of modern microscopy and computational techniques to read out nm and $\mu$m-sized damage features produced by interactions of Dark Matter and neutrinos with nuclei of minerals. Natural minerals should have accumulated these minute features over Myrs, allowing us to...
We study numerically a combined gravitational and nonlinear magnetic lensing effect on electromagnetic flux. A magnetar with a dipole magnetic field and background gravitational field is considered to deflect the light rays which passed through its magnetosphere. We assume a square wave front as a grid with the dynamic step. At the nodes of this grid, the rays enter perpendicularly into the...
Quantum gravity has yet remained elusive from an observational standpoint. In this talk, I will discuss Swerves, a proposal within quantum gravity phenomenology that predicts testable effects in cosmological data. Motivated by considerations in Causal Set Theory, a discrete approach to quantum gravity, we have formulated the covariant Brownian motion of free particles around their geodesics....
This presentation delves into the study of 'hairy' black holes within the framework of Einstein scalar Maxwell gravity and Einstein scalar Gauss-Bonnet theories, with a focus on revealing new scalarized black hole solutions. We revisit established scalarization phenomena and venture into new solution territories, particularly highlighting the blend of linear and non-linear scalarization in...
Galaxy clusters are the most massive gravitationally bound systems consisting of dark matter, hot baryonic gas and stars. They play an important role in observational cosmology and galaxy evolution studies. We develop a deep learning model for segmentation of Sunyaev-Zeldovich (SZ) signal on ACT+Planck intensity maps and construct a pipeline for microwave cluster detection in the ACT...
Millisecond pulsars (MSPs) are fast-spinning neutron stars formed in binary systems through mass-accretion from a companion star. A large fraction are found in star clusters, such as globular clusters, whose high stellar densities create a collisional environment in which 2 and 3-body gravitational interactions are promoted. These interactions are responsible not only for the formation of a...
This talk presents a summary of both sessions on the Galactic Center.
We explore the class of stationary, axisymmetric, and asymptotically flat spacetimes describing charged black holes in general relativity combined with nonlinear electrodynamics, or reflecting the influence of dark matter, or in so-called parameterized dirty Kerr spacetimes, and test them using the observational data of both hot-spot and the high-frequency quasi-periodic oscillations detected...
We present the structure of a low angular momentum accretion flows around rotating compact objects incorporating relativistic corrections up to the leading post-Newtonian order. To begin with, we formulate the governing post-Newtonian hydrodynamic equations for the mass and energy-momentum flux without imposing any symmetries. However, for the sake of simplicity, we consider the flow to be...
If two particles move towards a black hole and collide in the vicinity of the horizon, under certain conditions their energy Ec.m. in the center of mass frame can grow unbounded. This is the Banados-Silk-West (BSW) effect. Usually, this effect is considered for extremal horizons and geodesic (or electrogedesic) trajectories. We study this effect in a more general context, when both geometric...
Big Bang Nucleosynthesis provides us with an observational insight into the very early Universe. Since this mechanism of light element synthesis comes out of the standard model of particle cosmology which follows directly from General Relativity, it is expected that any modifications to GR will result in deviations in the predicted observable parameters which are mainly, the neutron-to-proton...
In a growing number of recent works, it has been claimed that "gravitomagnetism"/frame-dragging and/or non-linear general relativistic effects can play a leading role in galactic dynamics, partially or totally replacing dark matter. Using the 1+3 "quasi-Maxwell" formalism (and generalizing it for null geodesics), we show, on general grounds, such hypothesis to be impossible. We demonstrate...
This paper reports a stochastic theory of gravitational relaxation based on a Lévy-fractional Klein-Kramers equation with self-consistent entropy term. The use of fractional derivatives in this equation is motivated with nonequilibrium phase-space dynamics breaking the restrictive assumptions of Gaussianity, lack of correlation and nearness to virialized state. Astrophysical applications of...
Measurements of the Hubble-Lemaitre constant $H_0$ require us to estimate the distance and recession velocity of galaxies independently. Gravitational clustering that leads to the formation of galaxies and the large scale structure leaves its imprints in the form of peculiar velocities of galaxies. In general, it is not possible to disentangle the peculiar velocity component from the recession...
The Einstein–Maxwell and the electrodynamical equations are written for a (d+1)-dimensional FRW-like spacetime in the presence of plasma with the help of a wellknown (3 + 1) decomposition formalism given by Thorne and Macdonald. Actually this work is the generalisation of earlier one by Holcomb and Tajima[2].
We have studied the propagation of an electromagnetic wave in cold plasma in...
In this presentation, I will discuss about the unhindered gravitational collapse of spatially homogeneous (SH) scalar fields $\phi$ with a potential $V_{s}(\phi)$, as well as vector fields $\tilde{A}$ with a potential $V_{v}(B)$ where $B=g(\tilde{A},\tilde{A})$ and $g$ is the metric tensor. If the past end-point of a causal geodesic is a singularity, then this singularity is said to be naked....
Using a set of general-relativistic magnetohydrodynamics simulations that include proper neutrino transfer, we assess for the first time the role played by the fallback accretion onto the remnant from a binary neutron-star merger over a timescale of hundreds of seconds. In particular, we find that, independently of the equation of state, the properties of the binary, and the fate of the...
Fast Radio Bursts are millisecond-duration bursts of radio waves arriving generally from cosmological distances. Their nature remains unknown. Here I will review the latest on what is known about this mysterious phenomenon, concentrating on what has been learned from the CHIME telescope, a digital radio telescope operating in Canada, that offers an unprecedented view of the FRB population.
With the detection of multiple neutron-star merger events in the last few years, the need for a more comprehensive understanding of nuclear and atomic properties has become increasingly important. Despite our current understanding, there are still large discrepancies in the opacities obtained from different codes and methods. These discrepancies lead to variations in the location and strength...
In Einstein’s general relativity, extremely strong gravity can trap light. In a spacetime admitting a singularity, we say that light (or a “photon”) is trapped if it neither escapes to spatial infinity nor falls into the singularity. Null geodesics govern the trajectories of light. In the Schwarzschild spacetime with positive mass $M$, there exist (unstable) circular orbits of trapped photons...
We propose a model of the gravitational collapse of dark matter in the presence of dark energy, modeled by quintessence or phantom-like scalar fields. This work is based on the principles of general relativity up to virialization. We have chosen a spherical patch that starts to collapse gravitationally, as occurs in top-hat collapse. It is observed that although the dark matter sector...
In the space gravitational wave detection program, the locking and releasing of test mass is one of the key technologies. The test mass is locked in during the launch phase of the spacecraft and then released during the scientific exploration phase, allowing it to go into free fall. Among them, the residual release impulse of the test mass is required to be in the order of magnitude of 10-5 kg...
We have systematically presented the effect of the Generalized Uncertainty Principle (GUP) in Casimir wormhole space-time in the recently proposed modified gravity, the so-called symmetric teleparallel gravity, or $f(Q)$ gravity. We consider two famous GUP models, such as the Kempf, Mangano, and Mann (KMM) model and the Detournay, Gabriel, and Spindel (DGS) model, in this study. Also, to find...
In this work, we investigate the high-energy emission in SGRs/AXPs, neutron stars with extreme magnetic field, named magnetars. The observed high-energy emission in the X-rays and gamma-ray bands are explained. The outer gap accelerator model considers the generation of high-energy emission far away from the surface of the star in a combination of curvature radiation and inverse Compton...
The INTEGRAL hard X-ray surveys have proven to be of fundamental importance. In more than twenty years of operation, the INTEGRAL observatory has given us a sharper view of the hard X-ray sky, and provided the triggers for many follow-up campaigns from radio frequencies to gamma-rays. In addition to conducting a census of hard X-ray sources across the entire sky, INTEGRAL has carried out...
As the last student of Prof. Malheiro I would like to talk about him and present my work which he was involved in his last year of his life:
The study of Active Galactic Nuclei (AGN) has garnered significant attention due to their structures and dynamic behaviors. Understanding AGN feedback mechanisms and their impact on host galaxies is of paramount importance. In this context, the TWIST...
I will review the properties of kilonova host galaxies, focusing in particular on kilonovae detected from their associated gamma-ray burst component. A special consideration will be devoted to the physical properties of KNe, such as the offset from their hosts, and considerations on their formation channels.
Strong gravitational lenses are massive cosmic objects, like galaxies or galaxy clusters, which can map an extended background source, like a galaxy, into several highly distorted and magnified images. Analysing the properties of those images yields important information about the distribution of the deflecting mass and the background source. Common approaches to reconstruct the source or the...
Understanding the intricate network of nonlinear interactions crucial for the development and sustenance of turbulence induced by magnetorotational instability (MRI) has proven challenging. A large-scale dynamo, generating dominant azimuthal magnetic fields, emerges as a pivotal component of this turbulence. Direct numerical simulations of MRI dynamo have revealed statistical self-organization...
The large-scale structures such as Fermi Bubbles and eROSITA Bubbles provide a unique opportunity to study our Milky Way. However, the nature and origin of these large structures are still under debate. In this talk, I will present the identification of several kpc-scale magnetised structures based on their polarized radio emission and their gamma-ray counterparts, which can be interpreted as...
We investigate whether there are evidences for the existence of a new tension on the matter density parameter, independent or in relation with the Hubble or the matter fluctuation parameter tension, and that using a combination of multiple probes in a model independent approach where we relax most of the calibration parameters related to the aforementioned discrepancies.
Astrometric data presented in ATNF Pulsar Catalogue have enabled us to determine the trajectories through
the Galactic potential for different kick-velocity models of pulsars.
The system was disrupted ~0.2-0.8 Myr ago, which must correspond to the true age of at least one of the pulsars.
The implied pulsar birth velocities are consistent with the high velocities of neutron stars in...
Type Ia Supernovae (SNe Ia) are considered the most reliable standard candles and they have played an invaluable role in cosmology since the discovery of the Universe's accelerated expansion. During the last decades, the SNe Ia samples have been improved in number, redshift coverage, calibration methodology, and systematics treatment. These efforts led to the most recent "Pantheon" (2018) and...
Inspired by the pioneering 1968 work of L Parker, demonstrating matter quanta production in a dynamical spacetime background, we consider production of scalar quanta in a gravitational wave background. Choosing the spacetime to be a flat spacetime perturbed linearly by a linear gravitational wave, we show that scalar particles may indeed be produced in a perturbative manner. Our formulation is...
The existence of a relic neutrino backgorund (R$\nu$B) is a major prediction of the standard cosmological model, but its detection is one of the hardest tasks in neutrino physics. The main challenge arises because of its extremely low energy, as a consequence of its low temperature $T_\nu \simeq 1.67\times 10^{-4}\,\text{eV}$. The most promising experimental technique to detect the R$\nu$B is...
We present the results of a comprehensive spectro-polarimetric analysis of nine black hole X-ray binaries namely Cyg X$-1$, 4U 1630$-47$, 4U 1957$+115$, Cyg X$-3$, LMC X$-1$, LMC X$-3$, Swift J1727.8$-1613$, Swift J151857.0$-572147$ and GX 339$-4$ using quasi-simultaneous IXPE, NICER and NuSTAR observations. Polarimetric measurements with IXPE confirm the detection of a significant degree of...
Stochastic (i.e. the achromatic component of timing noise unrelated to interstellar propagation) and secular variations in the spin frequency $\nu$ of a rotation-powered pulsar complicate the interpretation of the measured second derivative of the spin frequency $\ddot{\nu}$, and hence the braking index, $n$, in terms of a power-law spin-down torque $\propto \nu^{n_{\rm pl}}$. Both...
We develop a framework to study the properties of mass outflows from a relativistic, viscous, magnetized, advective accretion flow around a rotating black hole (BH). While doing so, we assume that the disk is mainly threaded by the toroidal component of magnetic field and consider synchrotron radiation as the main cooling mechanism within the accretion disk. With this, we self consistently...
The aim of our work is to study the origin of the spectral transitions of transient black hole binaries. In this work, we find signatures of spectral state transition (hard to soft state) while studying the radiative shock forthe accretion flow. The gradient of the energy dissipation curve shows a sudden break for certain critical flow parameters when the post-shock dissipation is maximum....
We investigate the properties of relativistic accretion flow in a Kerr-Taub-NUT (KTN) spacetime in presence or absence of shock waves. This spacetime, characterized by the spin parameter or Kerr parameter ($a_{\rm k}$) and the gravitomagnetic charge or NUT parameter ($n$), can represent either a black hole or a naked singularity depending on the suitable choice of their values. By solving the...
The fast variability properties of Galactic black holes binaries can be satisfactorily explained by considering multiple physical mechanisms, such as Comptonization, reflection, variation in accretion geometry, focusing due to gravitational bending, and the effect of disk-jet connections. The nature of variability i.e., soft/hard time lag in Black Hole Transients, is complex due to the...
Our understanding of the mass distribution of white dwarfs remains elusive, yet it stands as a fundamental aspect of these stellar remnants that mark the final stage of the majority of stars' lifecycles. Unravelling this distribution requires untangling the influences of the initial mass function, star formation history, and stellar evolution. The latter can be significantly altered by the...
Despite of the key role of Type Ia Supernovae in cosmology and after decades of research, the nature of their progenitors remains unclear. None of the results obtained so far is sufficiently conclusive and, in some cases, the findings appear to be even in contradiction. Moreover, observations have shown that about 30% of the discovered SNe Ia largely deviate from the properties of 'normal'...
Large frame Ring Laser Gyroscopes which operate based on the Sagnac effect, are highly sensitive instruments used to measure angular velocity relative to fixed stars. The GINGER (Gyroscopes IN GEneral Relativity) project plans to build an array of three large Ring Laser Gyroscopes, firmly attached to the Earth. GINGER aims to detect General Relativity effects and potential Lorentz Violation in...
Alternate Theory of Time along with numerical proof.
The wave function for a closed de Sitter universe has been computed, demanding consistency with the recently proposed Trans-Planckian Censorship Conjecture (TCC). We extend the Einstein-Hilbert action to contain a complex-valued term which provides an exponentially decaying weight for the geometries violating TCC in the Lorentzian path integral sum while working in the minisuperspace approach...
