The Sixth Zeldovich meeting
ICRANet, Pescara, Italy
A series of international meetings in honor of Ya. B. Zeldovich
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Sunyaev-Zeldovich effect and cosmologyConvener: Roland Walter
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OpeningSpeaker: Remo Ruffini (ICRANet, ICRA, INAF)
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Little Red Dots as Sites for Cosmic Prebiotic Chemistry
Both the Galactic Center and little red dots (LRDs) host million-solar-mass black holes within dense, cold reservoirs of molecules associated with dust grains, and are electromagnetically tranquil. These conditions enable complex molecular chemistry and may serve as natural laboratories for prebiotic genetic evolution by allowing the synthesis of organic molecules essential for life.
Speaker: Yu Wang (ICRA/ICRANet/INAF) -
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The LSST era: opportunities, challenges, and simulations for AGN science
The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will open a new window on the dynamic Universe, delivering deep, multi-band, time-domain observations over a large fraction of the sky. Its combination of depth, area, cadence, and wavelength coverage will have a major impact on many areas of astrophysics, from Solar System studies to cosmology and galaxy evolution.
I will give an overview of LSST and then focus on active galactic nuclei, for which LSST will provide a unique view of variability, accretion processes, and the demographics of growing supermassive black holes across cosmic time. I will discuss challenges such as the identification and classification of AGNs from photometry and variability alone, which require robust selection methods and a careful understanding of observational biases and systematics.
I will conclude by discussing the role of simulations in preparing for LSST AGN science, with particular emphasis on AGILE: AGN In the LSST Era, an end-to-end simulation framework developed as part of the INAF LSST in-kind contribution. I will briefly discuss how AGILE can support LSST AGN science by testing selection strategies, quantifying biases, and helping interpret the first LSST data.Speaker: Angela Bongiorno (INAF-Observatory of Rome) -
10:45
Coffee break
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22 years of work with my Great Mentor Yakov Zeldovich
- from CMB cosmology and the theory of accretion onto black holes and neutron stars to four Orbital X-Ray Observatories and results of ground-based submillimeter and mm observations.
Speaker: Prof. Rashid Sunyaev (Max Planck Institute for Astrophysics, Garching and Space Research Institute, Moscow) -
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The Atacama Cosmology Telescope: Two Decades of Precision Cosmology
Since its conception in the early 2000s, the Atacama Cosmology Telescope (ACT) has played a leading role in transforming the Cosmic Microwave Background into a precision probe of fundamental physics and structure formation. From the first observations in 2007 through the successive ACTPol and Advanced ACTPol upgrades, ACT has pioneered a wide range of measurements, including the first detection of CMB lensing, early evidence for dark energy using CMB data alone, and the first detection of the kinetic Sunyaev–Zel'dovich effect. Over nearly two decades, the collaboration has delivered a wealth of results spanning cosmological parameters, galaxy clusters, large-scale structure, gravitational lensing, neutrino physics, and millimeter-wave astrophysics.
In this talk, I will review the scientific history of ACT, highlighting the key instrumental developments and some of its most significant discoveries. I will discuss the final data releases, which provide state-of-the-art maps, spectra, lensing reconstructions, and cosmological constraints, and reflect on ACT's enduring scientific legacy as the collaboration continues to produce new results. ACT represents not only a major chapter in observational cosmology, but also a bridge between the era of WMAP and Planck and the next generation of experiments, including the Simons Observatory.Speaker: Elia Stefano Battistelli (Spaienza University of Rome) -
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Next Frontiers in Cosmology with CMB Spectral Distortions
Spectral distortions of the Cosmic Microwave Background (CMB) are one of the next frontiers in CMB cosmology. In my talk I will give a broad brush overview of some of the exciting developments, highlighting what information might be extracted by studying CMB spectral distortions and how we can learn about inflation and particle physics using this new probe.
Speaker: Jens Chluba (JBCA) -
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The Kinematic Sunyaev-Zeldovich Effect as a Test of Gravity
The inverse-square law of gravitation has been tested from microscopic to solar system scales. However, directly probing gravity at galactic and cosmological scales remains a challenge. At galactic scales, the missing mass dominates rotation curves, while extragalactic tests often depend on the assumed expansion history of the universe. These dependencies complicate model-agnostic tests of theories of gravity that seek to explain these phenomena without invoking dark matter. In this talk, I present the pairwise kinematic Sunyaev-Zeldovich (kSZ) effect (the Doppler-shifted Compton-scattered light of the cosmic microwave background) as a direct, model-independent probe of the gravitational force law. We show that modified gravity models capable of reproducing the observed correlation function of galaxies may still fail to predict their mean pairwise velocity. Using data from the Atacama Cosmology Telescope and the Sloan Digital Sky Survey we constrain the exponent n of the gravitational force scaling, g \propto r^{-n}. Our analysis covers distances from tens to two-hundred megaparsecs, representing the largest scale test of the gravitational force law to date. I will discuss how upcoming CMB surveys such as the Simons Observatory large aperture telescope, paired with large spectroscopic catalogs of galaxies such as DESI are poised to probe gravity with 10σ significance, establishing the kSZ effect as a probe of gravity.
Speaker: Patricio Gallardo (University of Pennsylvania)
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Sunyaev-Zeldovich effect and cosmologyConvener: Volker Perlick
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Fractal properties of the Cosmic Web
I provide a review of the fractal properties of the cosmic web. Extreme views on fractal properties were expressed by Pietronero and Davis. To get an unbiased view on fractal properties I describe fractal function found from angular 2D and spatial 3D distributions of galaxies, using numerical simulations and SDSS samples of galaxies in a box of side length 512 Mpc/h. To measure the fractal dimension, I use the structure function 𝑔(𝑟) = 1 + 𝜉(𝑟), and its log-gradient. 𝛾(𝑟). The fractal dimension function, 𝐷(𝑟) = 3 + 𝛾(𝑟), of 3D samples characterizes the structure of halos on small separations, 𝑟 ≤ 4 Mpc/h, and the distribution of galaxies in filaments on larger separations. Fractal dimension functions of 2D samples depend on the thickness of samples, L. In SDSS and simulated Millennium galaxy samples the internal structure of halos is invisible. The analysis shows that both Pietronero and Davis views have correct as well as wrong properties.
Speaker: Jaan Einasto (Prof.) -
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MOND: An alternative to particle dark matter
Milgromian dynamics (or Modified Newtonian Dynamics, MOND) is a major alternative to particle dark matter proposed in 1983 by Mordehai Milgrom. MOND modifies the non-relativistic laws of gravity and/or inertia at low accelerations, below a characteristic acceleration scale a0. In this invited talk, I will showcase the content of the first "MOND white paper" which results from the collaboration of more than 60 researchers across the globe working on different aspects of MOND. This white paper covers fundamental theories, numerical simulations, and observational tests of MOND across all astronomical scales, from the Solar System to Cosmology. In particular, I will focus on the successful a-priori predictions that MOND made on galaxy scales, as well as the long-standing problems it faces in galaxy clusters. I will also mention recent relativistic extensions of MOND that allow reproducing the cosmic microwave background, the linear matter power spectrum, and the observed behavior of gravitational waves.
Speaker: Federico Lelli (INAF - Arcetri Astrophysical Observatory) -
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New Discovery Space in Gravitational-wave Astronomy from Model- agnostic Analysis
The emerging field of gravitational-wave astronomy opens a new window onto extreme transient sources in the Local Universe. Realizing this potential calls for model-agnostic data analysis operating at detector-limited sensitivity through advanced signal processing. We discuss Butterfly Matched Filtering (BMF), a broadband matched-filter search over dense bank of symmetrized chirp-like templates that circumvents the time-frequency uncertainty inherent to FFT-based analyses.
Applying BMF to LIGO/Virgo data, we identified a descending ravitational-wave chirp, GW170817B, following the binary neutron star merger GW170817, at 5.5σ significance from consistent and independent H1 and L1 detections. GW170817B subsequently unveiled, through GW calorimetry, a black-hole central engine powering GRB170817A. By universality of black holes, mass-scaling from this result indicates a search horizon capable of revealing the central engines of energetic core-collapse supernovae out to and beyond 160 Mpc, instead of the conventional few Mpc, with the current generation of gravitational-wave detectors — a reach comparable to that for binary neutron star mergers.
This capability opens a radically new discovery space in gravitational-wave astronomy. Implemented at exascale, these signal-processing methods are of particular interest for next-generation detectors such as the Einstein Telescope.Speaker: Maurice Van Putten (Sejong University) -
16:30
Coffee break
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Coherence-Regulated Structure Formation in Kalpa-Self-Regulating Cosmology (Kalpa-SRC)
We discuss a perturbative and thermodynamic extension of Kalpa-Self-Regulating Cosmology (Kalpa SRC), in which cosmic evolution is governed by self-regulating departures around a preferred equilibrium state characterized by an euation of state $w = -1/3$. Different from conventional cyclic or rebouncing cosmologies, Kalpa-SRC describes a globally, monotonically expanding universe evolving through successive non-singular kalpas (cosmic phases) connected by localized geometric phase transitions. In the current construction, the dark sector is modeled as a single equilibrium regulated medium containing coherent clustering and relaxation phases. Structure formation is therefore governed not only by the traditional gravitational instability alone, but also by coherence propagation and relaxation-mediated transport within a near-critical cosmological medium. The resulting perturbative reconstruction supplements standard radiation-era transfer evolution with finite coherence filtering and dynamically regulated transport. The framework trends naturally toward enhanced early structure formation, preserved halo growth, moderated late-time clustering amplitudes, and elevated late-time expansion rates. Representative internally consistent semi-analytic benchmark reconstructions yield viable current values for $H_0$, $\sigma_8$, $S_8$; and $f\sigma_8$, while simultaneously exhibiting mild equilibrium-regulated late-time flattening behavior that is qualitatively relevant to recent evolving-expansion discussions motivated by DESI observations. More broadly, Kalpa-SRC suggests that inflation, radiation production, dark-sector evolution, structure formation, and cosmic acceleration may all represent dynamically coupled phases of a single self organizing cosmological medium undergoing large-scale equilibrium-seeking regulation. The present work establishes perturbative viability, observational plausibility, and theoretical considerations for coherence regulated structure formation, within the Kalpa-SRC framework.
Speaker: Manasse Mbonye (University of Rwanda) -
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The Sunyaev-Zel'dovich (SZ) effect in a gravitational field
The influence of the plane gravitational wave on the CMB spectral distribution is studied. In the context of the kinematic SZ effect the distribution maximum is found to be shifted to the soft spectrum range due to the changes of the space-time metrics. The contribution of soft photons generated by charged particle in the field of a gravitational wave into the CMB is derived (the thermal SZ effect). We show that such a contribution leads to changing the CMB spectrum, broadening its shape.
Speaker: Andrew KOSHELKIN (In person, Moscow, Russia) -
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Spacetime foam correlation renders the cosmological constant (dark energy)
Wheeler's spacetime foams (wormholes) at the Planck length undergo quantum nucleation, oscillation and annihilation. Their collective excitations over foamy spacetime interact with field operators at large distances. We describe such collective excitation and interaction using an effective ``foamon'' field coupled with field operators. The Wilson renormalisation group approach shows that the foamon field theory evolves from an infrared scaling invariant domain to an ultraviolet one, when numerous particles are present. In these domains, the foamon field induces an effective action of field operators, and its correlation length sets a natural scale. Applying this to cosmology, we obtain the effective Einstein action for the Ricci scalar and the cosmological constant (dark energy), including its equation of state and interaction with matter.
Speaker: Prof. She-Sheng Xue (ICRANet, Physics Department, Sapienza University of Rome) -
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Constraining Inflation Models with Spinning Voids
We present a powerful new diagnostics by which the running of scalar spectral index of primordial density fluctuations can be tightly and independently constrained. This new diagnostics utilizes coherent rotation of void galaxies, which can be observed as redshift asymmetry in opposite sides dichotomized by the projected spin axes of hosting voids. Comparing the numerical results from the AbacusSummit of cosmological simulations, we derive a non-parametric model for the redshift asymmetry distribution of void galaxies, which turns out to be almost universally valid for a very broad range of cosmologies including dynamic dark energy models with time-dependent equation of states as well as the $\Lambda$CDM models with various initial conditions. We discover that the universality of this model breaks down only if the running of scalar spectral index deviates from zero, detecting a consistent trend that a more positive (negative) running yields a lower (higher) redshift asymmetry of voids than the model predictions. Given that non-standard inflations usually predict non-zero runnings of the spectral index and that the redshift asymmetry distribution of voids is a readily observable quantity, we conclude that this new diagnostics will pave another path toward understanding the true mechanism of inflation.
Speaker: GeonWoo Kang (Seoul National University) -
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Indications of relevant quantum corrections for cosmological parameters from unimodular quantum cosmology
Providing a natural time, unimodular quantum cosmology admits the description of quantum dynamics by a Schrödinger like equation for the wavefunction of the universe. The interplay of growing uncertainties and deviations from classical orbits yields late-time correction terms for the Hubble parameter and the matter density. These quantum correction terms are induced by quantum uncertainties that are proven to accumulate with time if specific conditions on the trajectories of the corresponding classical dynamical system apply. The explicit calculation of the expectation value of the Hubble parameter for a quantum analogue of a de-Sitter universe gives a first hint which kind of quantum corrections can be expected for the cosmological standard model.
Speaker: Dr Natascha Riahi (University of Vienna)
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What is possible to see in principle from the next exoplanet? (public lecture)Speaker: Roland Walter
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Observations across electromagnetic spectrum: from gamma to radioConvener: Taghi Mirtorabi
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UPE Self-Similarity in Gamma-Ray Bursts: A Comparative Study of Thermal Plus Nonthermal Continuum Prompt Emission
Gamma-ray bursts (GRBs) exhibit remarkable diversity in their prompt emission, yet certain spectral features recur across different events. In this presentation we examine the phenomenon of ultrarelativistic prompt emission (UPE); a short, highly luminous keV–MeV interval characterized by a thermal component superimposed on a nonthermal continuum, in a sample of eight GRBs spanning a wide range of durations and energies. The analysis reveals that this spectral form persists under successive temporal subdivision, establishing an empirical self-similarity in the MeV emission. The recurrent UPE state, observed from the short GRB 090510 to the exceptionally energetic GRB 160625B, provides a robust observational constraint for emission models and points to fundamental physical processes, including pair-plasma transparency and the role of overcritical electromagnetic fields, as key ingredients in the prompt emission mechanism.
Speaker: Rahim Moradi (ICRANet and ICRA-Sapienza) -
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The UPE of GRB 220101A
We will discuss the physics of the ultrarelativistic prompt emission (UPE) phase of GRB 220101A driven by electron positron pairs produced by QED vacuum breakdown.
Speaker: Jorge Armando Rueda Hernandez (ICRANet) -
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The physics of fast radio bursts
I review the recent progress in studying gamma-ray bursts (GRBs), fast X-ray transients (FXTs), and fast radio bursts (FRBs) within the context of multi-wavelength (MW) and multi-messenger (MM) transient astrophysics. Special attention is paid to the breakthrough observations made with the Einstein Probe, SVOM space telescopes, and the FAST radio telescope. Current understanding and open questions in these areas will be highlighted, with a discussion of the prospects of making further progress in the upcoming decade.
Speaker: Bing Zhang (University of Hong Kong) -
10:45
Coffee break
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Galileo, Hertz and the "Time Frontier"
Modern physics and astronomy both originated from Galileo. Hertz invented the first antenna and demonstrated the wave-particle duality of light. These developments give rise to radio astronomy and giant dishes. The Parkes multi-beam system transformed single-dish radio astronomy, delivering the largest haul of new pulsars, definitive HI galaxy catalogues, and the standard HI maps of the Southern sky. These landmark surveys had to be conducted separately, due to the conflicting observation requirements. We invented the high-cadence CAL technique, in which the calibration signal is injected at the sampling rate and facilitate, for the first time, truly commensal pulsar and spectral-line surveys. Implemented on FAST with drift-scan mode, the Commensal Radio Astronomy FAST Survey (CRAFTS) has discovered more than 230 pulsars and 10 FRBs, and released over 5,000 square degrees of calibrated HI images. I will report a few science highlights from CRAFTS, in the context of surveying the radio sky. The experience of setting up high-cadence surveys also lead to a few recent discoveries, including the first radio pulsar from a Central Compact Object (CCO) and the first long-period-transient (LPT) associated with a supernova remnant. CRAFTS' high cadence sampling of the radio sky also give rise to the concept of the "time frontier". I coined this term to represent the quantum foundation of the Universe that is to be revealed by exploring extreme transients. Hypothetical considerations will be given to possible lines of investigations.
Speaker: Prof. DI LI (Department of Astronomy, Tsinghua University) -
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20 years of testing GR with the Double Pulsar
Pulsars are extremely stable natural clocks and, when found in relativistic binary systems, they can be used as exceptional laboratories to test Relativistic gravity in the strong field regime. In this talk I will present the results obtained in this context by studying the now 20-year-long dataset on the double pulsar system J0737-3039A/B, the only binary hosting two active radio pulsars, and one of the most relativistic systems known to date. The double pulsar laboratory has indeed allowed us to confirm the validity of GR at least at 99.99% and to measure several relativistic effects for the first time.
Speaker: Marta Burgay (INAF - Osservatorio Astronomico di Cagliari) -
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A concordance picture of Tidal Disruption Event
A tidal disruption event (TDE) occurs when an ill-fated star ventures too close to a black hole. The intense gravitational forces of the black hole rip the star apart, sending roughly half of its mass hurtling into space, while the remainder falls back toward the black hole. This process produces a rich, multiwavelength observational signature—typically including an optical and ultraviolet flare lasting several months, accompanied by both prompt and delayed X-ray emission, and occasionally, a radio signal. Recent advances in theoretical models and, in particular, the consensus results of several simulations have significantly reshaped our understanding of the mechanisms behind TDE emission. In this talk, I will present key observational findings and explore how our perspective has evolved from earlier interpretations to current insights.
Speaker: Tsvi Piran (The Hebrew University) -
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X-ray polarimetry of black hole X-ray binaries – results and models
The Imaging X-ray Polarimetry Explorer (IXPE) has provided the first precise polarization measurements of black hole X-ray binaries, opening a new window on accretion and high-energy emission physics. In my talk, I will review recent IXPE results across different spectral states and discuss models used to interpret the observed polarization signatures. I will focus on what polarization reveals about the accretion flow geometry, the corona properties, and the origin of X-ray emission. Recent IXPE results offer new insights into the structure and dynamics of matter in the strong-gravity environment around black holes.
Speaker: Vadzim Krautsou (University of Turku)
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Compact objects and gravitational wavesConvener: Prof. She-Sheng Xue (ICRANet, Physics Department, Sapienza University of Rome)
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New insights on cosmic sources from X-ray polarimetry
The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on December 2021 (re)opened the window of X-ray polarimetry. In its first 4.5 years of operation IXPE observed objects belonging to almost all classes of X-ray sources, with a wealth of interesting and often surprising results. In this talk I will provide a (inevitably biased) review of IXPE results, and briefly discuss possible future X-ray polarimetric missions.
Speaker: Giorgio Matt (Roma Tre University) -
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High energy collisions in strong gravitational field: general approach
During last decade and a half many results are obtained that show when (i) particle collisions in a strong gravitational eld lead to an unbounded energy in the center of mass Ec:m: of two colliding particles, (ii) when the process leads also to signi cant energy extraction measured at in nity. The set of possible scenarios can be divided to three main cases: (i) collisions near black holes, (ii) near wormholes, (iii) near singularities Case (i) is mainly connected with what is called the Bañados-Silk-West (BSW) effect. We suggest a brief review of such processes. In doing so, we make an accent on recent developments and quite unexpected results. We include into consideration the presence of a force. Some general statement on possible or forbidden scenarios are formulated. In particular, it is shown that such collisions are possible even near the Schwarzschild horizon, provided a white hole or mirror region is included in consideration. It turns out that for collisions near black holes an unbounded energy extraction (so-called super-Penrose process) is impossible. However, this happens for collisions near wormholes.
Speaker: Prof. Oleg Zaslavskii (Kharkov V. N. Karazin National University) -
16:30
Coffee break
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Neutron and starnge stars in the uniform density approximation.
Models of neutron and strange stars are studied within the approximation of a uniform density distribution. A universal algebraic equation, valid for any equation of state, is used to estimate the stellar mass at a given density without resorting to the numerical integration of differential equations. Different equations of state for neutron stars had been used.
Homogeneous strange star models based on the quark bag model equation of state admit simple analytical solutions. The formation of strange stars is examined as a function of the deconfinement boundary (DB), at which quarks become deconfined. Existing experimental data indicate that matter reaches extremely high densities in the vicinity of the DB. This places strong constraints on the maximum mass of strange stars and their existence, when limiting mass of neutron stars is substantially higher and corresponds to significantly lower matter densities.Speaker: Gennady Bisnovatyi-Kogan (Space Research Institute Rus. Acad. Sci., Moscow, Russia) -
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Gravitational Refraction of Compact Objects with Quadrupoles
We use the material medium approach to derive the refractive index that can be associated with the gravitational field of a compact object with a quadrupole moment. We consider both a static deformation and a stationary rotation of the gravitational source as the source of the quadrupole. We show that up to the first order in the quadrupole, the refractive indices of both configurations are equivalent such that from the point of view of refraction, a mimicking effect can occur. This also holds at the level of the deflection angle. We argue that it is possible to use the refractive indices and the parameters of the trajectories of light rays that propagate in a gravitational field to determine the physical parameters of the source.
Speaker: Nurzada Beissen (Al-Farabi Kazakh National University, Almaty, Kazakhstan) -
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Anisotropic hybrid stars: Interplay of superconductivity and magnetic field leading to gravitational waves
Neutron stars, at their cores, are highly dense and, thus, are expected to have a number of exotic processes. This includes a possible phase transition to deconfined quark matter at the core, leading to a hybrid star. The quark matter is expected to additionally be color superconducting. The physics of superconductivity plays an important role in understanding the high density matter in the interiors of neutron/hybrid stars. At their high densities, additionally, both proton superconductivity and neutron superfluidity are expected. We study the effect of superconducting (quark/proton) matter, along with the internal magnetic field, leading to pressure anisotropy within hybrid stars. We aim to probe the effect of superconductivity, especially from color superconducting quarks, on hybrid star structure. We propose new phenomenological model anisotropy profiles within a one-dimensional framework. We model quark matter using the vector interaction enhanced Bag model, and hadron matter with the DD2 equation of state. A Maxwell construction joins both phases. We further investigate the possible observational signatures of these hybrid stars. These include mass enhancement and continuous gravitational waves, possibly arising from the anisotropy induced deformation, helping us further constrain our model and its physical parameters.
Speaker: Zenia Zuraiq (Indian Institute of Science, Bangalore) -
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Gravitational waves passing through matter
The interaction of gravitational waves (GWs) passing through matter is normally treated as being very weak. We have re-investigated this issue using linearized perturbations within the Bondi-Sachs formalism, with a model comprising a spherical shell of matter surrounding a GW source. We find analytic expressions for the GWs when the background is Minkowskian, but for a general spherically symmetric background the GWs are found numerically. If the matter in the shell has high viscosity, then the shear induced in the velocity field results in an energy transfer so damping the GWs and heating the matter. The effect is very weak when the matter is far from the GW source, but can be highly significant when the shell radius is less than the GW wavelength. The applications to astrophysics include supernova explosions, the quasinormal mode regime after a neutron star merger, and a binary black hole merger at which matter is present, as well as to primordial gravitational waves in cosmology.
Speaker: Prof. Nigel Bishop (Rhodes University) -
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On expectations of detection of gravitational waves originating from Core-collapse supernovae
Core-collapse supernovae
Expectations of detections of gravitational waves (GWs) originating from
core-collapse supernovae (CCSNe) have been growing. Whilst detections
with current interferometers limit the frequency range and also limit the
distance to that of galactic origin or its vicinity, estimates of detectable GWs
from CCSNe are of the order of a handful per century. This would seem
to indicate that we are long overdue for such a detection. It may be that
such events are buried in the data or could have been mis-characterised.
However, recent work done also indicates that a previously unaccounted for effect
could revise the expectation downward. Although GWs are, in general, not
expected to interact with matter, there are instances where the effect has to
be taken into account. In a series of investigations, we have shown the novel
result leading to viscous effects and gravitation wave heating in CCSNe.
These are scenarios that may diminish or altogether mask GWs from CCSNe
events. Our understanding of CCSNe events has undergone several revisions
in recent years and processes in the proto-neutron star (PNS) leading to
CCSNe are still not fully understood. GWs carry important information
that could illuminate the processes within the PNS and provide data on the
nature and composition of the core.Speaker: Monis Naidoo (Rhodes University; National Institute for Theoretical and Computational Sciences (NITheCS))
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Multi-messenger astrophysics (public lecture)Speaker: Bing Zhang (University of Hong Kong)
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Strong fields and dark matterConvener: Rahim Moradi (ICRANet and ICRA-Sapienza)
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GRB-SN Association within the Binary-Driven Hypernova Model
Observations of supernovae (SNe) Ic occurring after the prompt emission of long gamma-ray bursts (GRBs) are addressed within the binary-driven hypernova (BdHN) model, where GRBs originate from a binary composed of 10 solar masses carbon–oxygen (CO) star and a neutron star (NS). We report on recent progress in understanding the phenomenon and draw some prospects on GRB-SN research.
Speaker: Dr Yerlan Aimuratov (Fesenkov Astrophysical Institute) -
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A pulsar from the second Supernova in GRB 220101ASpeaker: Taghi Mirtorabi (Department of Fundamental Physics, Faculty of Physics, Alzahra University)
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Photon Acceleration in Magnetized Plasma: A Potential Source of Fast Radio Bursts
We propose a mechanism for fast radio bursts (FRBs) based on photon acceleration by relativistic shocks in highly magnetized electron-positron plasmas, as expected in magnetar magnetospheres. Density modulations at the shock front create relativistically moving refractive index perturbations that transform low-frequency electromagnetic precursors into enhanced high-frequency radiation. In magnetized pair plasmas, relativistically moving plasma layers exhibit enhanced reflectivity, while the maximum emission frequency is limited by the electron Larmor frequency. The observed frequencies, durations, and energetics of FRBs are reproduced for magnetic field strengths, spatial scales, and shock Lorentz factors consistent with those expected in magnetar magnetospheres. These results identify photon acceleration by relativistic magnetized shocks as a viable mechanism for FRB formation.
Speaker: Prof. Sergey Bulanov (ELI-ERIC, ELI BEAMLINES, Za Radnicí 835, Dolní Břežany, 25241, Czech Republic) -
10:45
Coffee break
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Demonstration of Nonlinear Compton Scattering in the Strongly Nonlinear Regime with Its Implications to High-energy Astrophysics
Nonlinear Compton scattering (NCS), the merging of multiple photons into one photon through collision with an energetic electron, is a fundamental process in strong-field quantum electrodynamics (SFQED). The degree of nonlinearity in NCS is quantified by the quantum nonlinearity parameter $\chi$,[1] defined as the electromagnetic field strength observed by the electron in its rest frame relative to the intrinsic field strength of QED, $E_S=1.3\times 10^{18} ~ \mathrm{V/m}$. In this regard, the condition $\chi=1$ serves as a critical milestone marking the transition from the weakly (perturbatively) nonlinear regime to the strongly (non-perturbatively) nonlinear regime. Consequently, the experimental realization of $\chi=1$ has been intensely pursued in the ultra-intense laser community to recreate such extreme physical conditions in the laboratory.
In this talk, we present recent experimental results obtained under the conditions $\chi=0.46$ [2] and $\chi=1.4$ at the Center for Relativistic Laser Science (CoReLS), reporting a definitive entry into the strongly nonlinear regime. In addition to the detailed analysis of these experimental results, we will discuss the broader implications of such laser-based SFQED research to high-energy astrophysics.[1] V. I. Ritus, “Quantum effects of the interaction of elementary particles with an intense electromagnetic field,” Journal of Soviet Laser Research 6, 497 (1985).
[2] M. Mirzaie et al., “All-optical nonlinear Compton scattering performed with a multi-petawatt laser,” Nature Photonics 18, 1212 (2024).Speaker: Chul Min Kim (Center for Relativistic Laser Science, IBS; and Advanced Photonics Research Institute, GIST) -
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Nuclear physics and astrophysics driven by intense lasers
Owing to the capability of providing extreme conditions such as extremely intense electromagnetic files and high-energy-density environments in the laboratory, high-power laser facilities offer powerful platforms for the studies of various research fields such as particle physics, nuclear physics, and astrophysics. In this talk, we will present and discuss our recent progresses on the studies of nuclear physics and astrophysics driven by intense lasers. Special focuses will be the studies of relevant nuclear excitation, as well as low-energy nuclear reactions with astrophysical interests.
Speaker: Yuanbin Wu (Nankai University) -
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Self-Confined Quarks: A General Relativistic Perspective on Strong Nuclear Forces
Abstract
Quarks, as spin-$1/2$ particles, can be described as Dirac spinors, and as massive entities, they are capable of curving their surrounding spacetime. We demonstrate that the general relativistic (GR) gravitation of quarks is sufficient to confine them within hadrons while allowing them to remain asymptotically free. Consequently, we conclude that strong nuclear forces and general relativistic gravitation are one and the same at the femtometer scales of quarks and hadrons.
I. INTRODUCTION
To the best of our knowledge, i) there is currently no established wave function for hadrons or their constituent quarks that parallels, for instance, Dirac waves for electrons, and ii) there is no definitive consensus as to what exactly nuclear forces are, except that they are strong and short-ranged.
In this paper, we assume that quarks, as massive entities, are capable of curving their surrounding spacetime. Furthermore, as spin-$1/2$ particles, they can be represented as Dirac spinors under proper normalization. We formulate the Dirac equation within a spherically symmetric and static spacetime, impose a Yukawa-like normalization, and solve it. Ultimately, we conclude that GR forces at femtometer scales are sufficiently strong to confine quarks within nucleons, while allowing them to be asymptotically free in the inner regions.
The standard Dirac matrices $\gamma^{\mu}$ are invariant under Lorentz transformations in flat spacetime; however, this invariance does not hold in curved spacetimes. In his detailed study [1], Alcubierre addresses this issue by transforming the $\gamma$-matrices into a spherically symmetric spacetime utilizing tetrad analysis to model a Dirac star. By formulating the Dirac equation in a spherically symmetric and static spacetime, he derives four coupled, first-order differential equations: two for the Dirac field and two for the spacetime metric coefficients. A Yukawa-normalizable version of Alcubierre's four coupled equations serves as our point of departure.
Herein, we provide a formal definition of the problem and design an iteration scheme to analyze it. We demonstrate how a spin-$1/2$ quark can be modeled as an Alcubierre-designed and Yukawa-normalized Dirac spinor. Finally, we derive the wave functions for quarks and nucleons and investigate the gravitational their manifestations. We conclude that the asymptotically flat spacetime inside a nucleon guarantees the asymptotic freedom of quarks, while the exponential falloff of the outer spacetime toward flatness ensures their confinement.
Dedicated to the International Year of Quantum Science and Technology (IYQST2025).REFERENCES
[1] M. Alcubierre, "The Dirac equation in general relativity and the 3+1 formalism" (2025), arXiv:2503.03918 [gr-qc].Speaker: Prof. Yousef Sobouti (Institute for Advanced Studies in Basic Sciences - Zanjan) -
38
SRG/eROSITA all-sky survey results in the Eastern Galactic hemisphere
After more than two years of scanning the sky during 2019--2022 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 that changed their luminosity by more than an order of magnitude, including about a hundred tidal disruption events. SRG/eROSITA samples of quasars and galaxy clusters will make it possible to study the large-scale structure of the Universe at z~1 and measure its cosmological parameters. I will review some of the SRG/eROSITA results in the Eastern Galactic hemisphere and future prospects.
Speaker: Prof. Marat Gilfanov (MPA, Garching & IKI, Moscow)
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Observations across electromagnetic spectrum: from gamma to radioConvener: Remo Ruffini (ICRANet, ICRA, INAF)
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The Northern Cross Fast Radio Burst project
In this talk I will review the Northern Cross FRB project, the ongoing effort to equip and use the Northern Cross (NC), the oldest Italian radio telescope, to observe FRBs. I will present the project's main results, highlighting the studies on known FRB repeaters and the population studies within our Galaxy and in a sample of star-forming nearby galaxies. Finally I will describe the future path, including the equipment of the 64 cylinders of the North-South arm and the upgrade of the East-West arm, which will lead to an effective FRB survey machine that will be complement other current facilities in the international panorama.
Speaker: Maura Pilia (INAF - Osservatorio Astronomico di Cagliari) -
40
X-ray and gamma-ray radiation from a high-temperature plasma and the spectra of accreting black holes
We present our numerical computations of the broadband radiation spectra forming in a layer of high-temperature ($kT_{\rm e}\sim 50$ keV) semitransparent (with a Thomson optical depth $\tau_{\rm T}\sim 1-3$) plasma with an electron density $N_{\rm e}\sim 10^{17}-10^{19}\ \mbox{cm}^{-3}$ typical for the accretion disk regions surrounding a black hole in X-ray binaries. The computations take into account the bremsstrahlung processes of photon production and absorption and their subsequent Comptonization. We show that the intrinsic radiation of such a high-temperature plasma is sufficient to explain the X-ray spectra observed in the low (hard) state of Galactic black hole candidates and X-ray novae. No commonly assumed additional soft (with energies $h\nu\leq 1$ keV) photons are required to maintain Comptonization; moreover, their presence would lead to severe distortions of the spectrum compared to the observed one or would require a very fine tuning of plasma parameters. In the hard X-ray range the forming power-law radiation spectrum with a photon index $\alpha\sim 1.4-1.7$ and an exponential cutoff at energies $h\nu\geq 100$ keV exceeds considerably the bremsstrahlung flux that might be expected from such a plasma layer in the limit of its very small optical depth. This is the result of the multiple inverse Compton scattering of bremsstrahlung photons. It is important that, according to our computations, the power-law radiation spectrum of such a high-temperature plasma should extend in an invariable form downward along the energy axis to the ultraviolet, optical, and infrared ranges ($h\nu\sim 1-3$ eV). At energies $h\nu\leq 1$ eV the optical depth for bremsstrahlung absorption grows rapidly and the radiation spectrum becomes the Rayleigh-Jeans one. To explain the steeper ($\alpha\sim 2.1-2.5$) X-ray spectra observed from accreting black holes in their high (soft or two-component) state, it is indeed necessary that a large number of soft photons additional to the intrinsic plasma bremsstrahlung photons enter a hot cloud. Such photons could be emitted by the surface of an outer dense and cold accretion disk whose inner edge during these states, characterized by a strong soft component in the X-ray spectrum, approaches the black hole as closely as possible. The optical and infrared emission from systems in these states is associated precisely with the emission from the outer disk, whereas during their low states, it can be produced directly in the hot central disk region bloated by instabilities. Under favorable circumstances (disk size and inclination) the low-frequency emission from this region can significantly exceed in flux and luminosity the emission from the outer cold accretion disk regions.
Speaker: Sergei Grebenev (Space Research Institute, Moscow) -
41
Dark Hydrogenic Atoms and Ions as Baryonic Dark Matter and their Role in Structure Formation
The explanation of a puzzling observation by Bowman et al 2018 (Nature, 555, 67) of the redshifted 21 cm spectral line from the early Universe, where it was found that the absorption in this line was about 2 to 3 times stronger than predicted by the standard cosmology and thus the primordial hydrogen gas was significantly cooler than predicted by the standard cosmology, required as the cooling agent, some kind of baryonic DM [Barcana, 2018 (Nature, 555, 71); McGaugh, 2018 (Res. Not. Amer. Astron. Soc., 2, 37)]. Then in paper [Oks, 2020 (Res. Astron. Astrophys. 20, 109)] there was given both qualitative and quantitative explanation of the puzzling observation by Bowman et al (2018) based on the specific DM in the form of the second flavor of hydrogen atoms (SFHA), corresponding to the 2nd solution of the Dirac equation for hydrogen atoms. In distinction to exotic hypothetical particles previously suggested as the explanation (the particles never discovered experimentally), the existence of the SFHA is evidenced by 3 different types of atomic experiments – plus it completely resolved the long-standing puzzle of the neutron lifetime. In the latter, the central point was that the two-body decay of neutrons produces – with the overwhelming probability – the SFHA rather than the usual hydrogen atoms. More details can be found, e.g., in my reviews on DM published in New Astronomy Reviews in 2021 (93, 101632) and in 2023 (96, 101673), and in my paper in Nuclear Phys. B 2025 (1014, 116879). The primary property of the SFHA is that, since they have only the S-states, then according to the selection rules of quantum mechanics they cannot emit or absorb the electromagnetic radiation: they remain dark. As the relation of these results to the structure formation in the universe, I provide the chronology of the cosmological formation of the surplus of the SFHA (compared to the usual hydrogen atoms) from the Recombination Epoch through the Structure Formation Epoch, including the production of the SFHA by some neutron stars. Therefore, the halos of modern galaxies contain more of the SFHA than the usual H-atoms. In addition, there is evidence from atomic experiments of the existence of the Second Flavor of He+ Ions (SFHeI). They are also dark due to the selection rules of quantum mechanics. There occurred the cosmological formation of the surplus of the SFHeI (compared to the usual He+) similarly to the surplus of the SFHA. Therefore, the halos of modern galaxies contain also more of the SFHeI than the usual He+. From atomic experiments follows that the most probable value of ratio (SFHA + SFHeI)/(usual H + usual He+) is 1.8. From astrophysical observations by de Graaff et al (2019, A&A, 624, A48) and by Penton et al (2004 ApJ Suppl. Ser. 152, 29) follows that the most probable value of the ratio (baryonic DM)/(luminous baryons) is 2.1. The comparison of these two ratios shows that the combination of the SFHA with the SFHeI most probably constitutes about 90% of all baryonic DM in the current epoch. It is important to emphasize that the discovery of the SFHA and the SFHeI was based on the standard Dirac equation of quantum mechanics without going beyond the Standard Model and without any change of physical laws – in distinction to the overwhelming majority of hypotheses on DM. Finally, I will discuss/motivate some relevant future laboratory experiments and astrophysical observations.
Speaker: Eugene Oks (Auburn University, USA) -
16:30
Coffee break
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42
The Higgs vacuum and the Cosmological Constant
We investigate the quantum dynamics of a spatially homogeneous quintessence field. It is thought that the ground state of the quintessence acts as the cosmological constant in the dynamical dark energy framework. The correlation function and power spectrum of quantum fluctuations exhibit ultraviolet divergence. To address this issue, we reformulate the system by interpreting quintessence as a lattice of rigidly coupled harmonic oscillators starting from $V(\phi)=m^2\phi^2/2$. Within this context, we apply the Heisenberg-Langevin formalism, incorporating both Hubble-induced damping and Markovian stochastic noise to effectively describe the dissipative quantum dynamics. We derive the corresponding ladder operators and determine the effective energy density. Finally, we generalize this formulation to encompass any arbitrary potential, thereby extending the utility of this framework to a wide range of dynamical dark energy models using quantum mechanics.
Speaker: Muhammad Usman (Institute of Space Technology (IST), Islamabad) -
43
Dynamical systems approach to teleparallel cosmologies
One of the most important open questions in cosmology is the so-called Hubble tension, which is an apparent disagreement between local universe measurements of the present-time Hubble parameter and measurements inferred from early-universe observations under the assumption of the $\Lambda$CDM model, which supplements general relativity (GR) with a cosmological constant $\Lambda$ and cold dark matter (CDM). Numerous modified theories have been studied in order to address this open question. While a large class of these models describes gravity as the curvature of spacetime, as it is the case in general relativity, an alternative class of theories employ a different mathematical background based on torsion and / or nonmetricity, while curvature is absent. In my talk I give an overview of such models and their cosmological dynamics. In particular, I will focus on quadratic teleparallel theories, which are motivated by their similarity to Yang-Mills theories, and thus share some common features with theories encountered in particle physics. To discuss the qualitative phenomenological features, I make use of the method of dynamical systems, which allows in particular studying the late-time behavior of the solutions. I will present several current results on cosmological attractor solutions.
Speaker: Manuel Hohmann (University of Tartu) -
44
Black hole shadows as diagnostics of nonlinear electrodynamics
We demonstrate how the shadow radius of regular black holes can serve as a powerful diagnostic tool for general relativity coupled with nonlinear electrodynamics (NED). By analyzing Bardeen-like, Hayward-like, and Maxwellian regular spacetimes, we highlight the critical distinction between standard null geodesics and the NED-driven effective photonsphere that governs light propagation. We show that the shadow radius carries distinct signatures of these field theories, acting as a sensitive probe for Lagrangian pathologies—evidenced by a unique discrepancy in the vanishing charge limit. Finally, using eikonal quasinormal modes, we confirm the robust correspondence between perturbations and the shadow size, proving it is strictly determined by the inverse angular velocity of the effective photonsphere.
Speaker: Dr Bobir Toshmatov (New Uzbekistan University) -
45
Significant correlation between optical activity of blazars and high-energy IceCube neutrino events
In 2013, neutrino observatory IceCube first reported discovery of high-energy (100 TeV and more) neutrinos of astrophysical origin. However, due to a bad spatial localization of these neutrinos (more than 1 arcdegree) origin of these neutrinoes stayed unknown. To find their progenitor, IceCube Collaboration organized multimessenger observations. Since 2016, IceCube Collaboration has published 183 public alerts on the detection of a high-energy neutrino event. One of the projects participating in these multimessenger observations is MASTER Global Robotic Net. Its nine telescopes spread all over the globe are able to rapidly slew on the neutrino event's location and have a wide FoV (2 by 2 arcdegrees), allowing it to find an optical counterpart of a neutrino event if any exists.
In 2017, IceCube detected a high-energy event named IceCube-170922A. It was subsequently found that a flaring blazar TXS0506+056 was located in the center of this event. Master telescope located in Crimea slew on its position 1 minute after the neutrino detection and it was found that blazar was 0.8 magnitude dimmer compared to observations a week before and an hour after the trigger. This finding led us to analyze the whole archive of our IceCube neutrino events observations to find if we had more of similar blazars. In this work we present an analysis of these observations and an excess of optically active blazars (flaring blazars and brighter than 15.2 mag) on a level of 4 sigma.Speaker: Kirill Zhirkov (Lomonosov Moscow State University) -
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Spontaneous creation/annihilation of pairs of particles in selected cosmological models –evolution of a vaccum state
In a large class of cosmological models quantization of a scalar free field leads to the picture of a system of harmonic oscillators coupled via terms corresponding to creation/annihilation of pairs of particles, obeying momentum conservation. In such a case, an evolution of a creation/annihilation operators, meant as a Bogolyubov transformation, may be regarded as a “rotation” in a two-dimensional, (k, -k) sub-space. One can argue, that if the Bogolyubov coefficients are found, then the evolution of an initial vaccum state may be described in a rigorous manner, even if it is a non-unitary evolution.
Evolution of multiparticle states will be discussed.Speaker: Prof. Andrzej Radosz (Institute of Theoretical Physics, Wroclaw University of Science and Technology, Wroclaw, Poland)
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Black holes and Penrose processConvener: Dr Yerlan Aimuratov (Fesenkov Astrophysical Institute)
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Black hole irreducible mass increase by particle accretion
We report on the increase in irreducible mass resulting from a particle’s plunge along the inner most stable circular orbit (ISCO) into a black hole (BH), examining both cases: the conservative approximation and with gravitational wave (GW) radiation; the former corresponds to BH accretion, and the latter to extreme mass-ratio inspirals (EMRIs). For prograde orbits, we find that the ratio of mass change to irreducible mass change is lower when GW radiation is taken into account than in the conservative case, while the opposite holds for retrograde orbits. Based on the differentiating changes in mass and irreducible mass, which are non-monotonic with respect to the spin, we derive the increasing curves of mass and irreducible mass. In the conservative case, after accreting up to three times its initial mass, the BH’s spin parameter reaches the extremal value $\hat{a} = 1$ and then enters a self-similar growth phase. When GW radiation is considered, however, the spin parameter does not reach the extremal limit but instead stabilizes near it. For the first time, we precisely determine this stabilization value and fit an analytical expression relating this stable value to the mass ratio.
Speaker: Shurui Zhang (ICRANet) -
48
Energy extraction from rotating black holes: electromagnetic and radiative Penrose processes
Rotating black holes provide a unique environment for extracting energy from spacetime rotation through processes occurring inside the ergosphere. In this presentation, I will review the classical Penrose mechanism and its electromagnetic extensions, with particular focus on the electric and magnetic Penrose processes. These mechanisms allow charged particles to gain energy through interactions with external electromagnetic fields, substantially increasing the efficiency of energy extraction compared with the original particle-splitting scenario. I will also discuss the radiative Penrose process, in which radiation reaction and electromagnetic emission contribute to particle acceleration and energy transfer. Finally, I will examine the observational predictions of these mechanisms and their application to various black hole candidates.
Speaker: Arman Tursunov (Silesian University in Opava and Max Planck Institute for Radio Astronomy) -
49
Black Hole─Halo Mass Relation from UNIONS Weak Lensing
This work presents, for the first time, direct constraints on the black hole─halo mass relation using weak gravitational-lensing measurements. We construct type I and type II active galactic nucleus (AGN) samples from the Sloan Digital Sky Survey, with a mean redshift of 0.4 (0.1) for type I (type II) AGNs. This sample is cross correlated with weak-lensing shear from the Ultraviolet Near Infrared Optical Northern Survey. We compute the excess surface mass density of the halos associated with 36,181 AGNs from 94,308,561 lensed galaxies and fit the halo mass in bins of black hole mass. We find that more massive AGNs reside in more massive halos. The relation between halo mass and black hole mass is well described by a power law of slope 0.6 for both type I and type II samples, in agreement with models that link black hole growth to baryon feedback. We see no dependence on AGN type or redshift in the black hole─halo mass relation below a black hole mass of 108.5 M ⊙. Above that mass, we find more massive halos for the low-z type II sample compared to the high-z type I sample, but this difference may be interpreted as systematic error in the black hole mass measurements. Our results are consistent with previous measurements for non-AGN galaxies. At a fixed black hole mass, our weak-lensing halo masses are consistent with galaxy rotation curves but significantly lower than galaxy-clustering measurements. Finally, our results are broadly consistent with state-of-the-art hydrodynamical cosmological simulations, providing a new constraint for black hole masses in simulations.
Speaker: Wentao Luo (USTC) -
10:45
Coffee break
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50
Near-horizon Polarization as a Diagnostic of Black Hole Spacetime
A key challenge in imaging supermassive black holes is disentangling gravitational effects from plasma physics in order to accurately determine spacetime properties, particularly black hole spin. In our recent work, we present a fully covariant and rigorous analysis of the synchrotron emission from accreting plasma in the equatorial plane in the stationary, axisymmetric, high-conductivity regime and identify—for the first time—a distinctive near-horizon polarization pattern that remains robust across different flow structures. This pattern arises from strong frame dragging near the event horizon, which induces a degeneracy among plasma flow and magnetic field configurations, yielding a polarization signature determined solely by the spacetime geometry and the observer’s inclination. The near-horizon polarization thus offers a clean and precise probe of black hole spin and other fundamental parameters. If future space-based millimeter very long baseline interferometry observations can resolve synchrotron emission originating within approximately 1% of the event horizon radius in M87 or Sgr A, this universal polarization pattern may become observable.
Speaker: Bin Chen (Ningbo University) -
51
Black holes in alternative theories of gravity
Black holes, with their strong gravitational fields, provide an important testing ground for theories of gravity beyond General Relativity. Among the many proposed alternatives, considerable recent work has focused on scalar-tensor theories in which a scalar field couples to higher-curvature terms. The black hole solutions that arise in such theories can differ significantly from the Schwarzschild and Kerr solutions of General Relativity. Characteristic properties of these black holes include instabilities, shadows, and gravitational wave spectra, which can be used to constrain the couplings of the underlying theories.
Speaker: Jutta Kunz (University of Oldenburg) -
52
Influence of a warm plasma on gravitational lensing by black holes
Analytical calculations of gravitational lensing by black holes and other compact or ultracompact objects, in particular of the shadow, were originally always done under the assumption that light rays are lightlike geodesics of the spacetime metric, i.e., that effects of a medium can be neglected. More recently the effect of a plasma was taken into account in numerous papers, where the plasma was always considered as being 'cold', i.e, its absolute temperature was treated as zero and its pressure was neglected. In this talk I review these earlier results and I generalise them to the case of a warm plasma, where the temperature is assumed to be non-zero but small enough such that the relevant equations can be linearised with respect to it. The temperature effects turn out to be small but possibly non-negligible in some cases of astrophysical interest. - This talk is largely based on joint work with Barbora Bezdekova, Haifa University, Israel.
Speaker: Volker Perlick -
53
The Global MASTER Network and the Scenario Machine: Discovery and Interpretation of the Third Optically Super-Luminous GRB in XXI century
Observation of this burst, which, based on its brightness, could have been detected by the Galileo telescope diameter, began 200 seconds before the burst itself. That is, before receiving alerts from the gamma-ray observatories. This means that the MASTER network is not only mobile but also has record-breaking combined field-of-view parameters (~4000 square degrees). This sheds new light on the problem of so-called precursors, a solution to which we are exploring within the framework of our proposed Spinar Paradigm.
Speaker: Prof. Vladimir Lipunov (Lomonosov Moscow State University, SAI, Physics Department)
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Gravity and black holesConvener: Jorge Armando Rueda Hernandez (ICRANet)
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Can the center of low-mass active galaxies be powered by dark matter?
The study of disc accretion physics around supermassive black hole (BH) candidates provides essential theoretical tools to test their nature. In this talk I present recent results about the accretion flow and associated emission using generalised α-discs accreting onto horizonless dark compact objects, and compare with the traditional BH scenario. The BH alternative consists in a dense and highly degenerate core made of fermionic dark matter (DM) which is surrounded by a more diluted halo able to explain the rotation curve according to the RAR model. The fact that the compactness of the dense DM core scales with particle mass, it leads to the following key findings: (i) There is always a given core compacity – corresponding particle mass – that produces a luminosity spectrum that is almost indistinguishable from that of a Schwarzschild BH of the same mass as the DM core. (ii) The disc can enter deep inside the non-rotating DM core,
allowing accretion-powered efficiencies of as high as 28%, which is comparable to that of a rotating Kerr BH. In addition, I will present new results using a key tracer of the space-time geometry of the central object: the fluorescent iron kα line and its broadening due to relativistic effects caused by the central DM core. Finally, I will show the possibility to extend this phenomenology to the full spectral energy distribution (SED) of low-mass AGN in the intriguing mass range of the central object of ~10^5-10^7 Msun.Speaker: Carlos Raúl Argüelles (Universidad Nacional de La Plata) -
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The closest environment of the supermassive black hole Sagittarius A* in X-rays
Long-term observations of the Galactic center in the X-ray band reveal a new picture of the stellar population in this densely populated region. This review will present recent studies of the region of supermassive black hole Sagittarius A using ultra-deep observations from the Chandra, Swift, and NuSTAR observatories. (1) An analysis of the X-ray spectra of more than a hundred sources within 5 parsecs of Sagittarius A revealed 13 non-thermal X-ray sources in the "central parsec" whose spectral and temporal characteristics indicate a population of quiet X-ray binaries with neutron stars (NSs) or black holes (BHs). The spatial distribution of 16 non-thermal sources (BH candidates) is consistent with the central stellar cluster, which confirms theoretical predictions about the formation of binary systems in the immediate environment of Sagittarius A. (2) Long-term monitoring of the Galactic center within a radius of 30 pc from Sagittarius A has revealed about 20 transients, including very faint transients and X-ray binaries with NS and BH. (3) The extended 10 pc emission from Sgr A, discovered by NuSTAR, indicates a population of white dwarfs with a mass of 0.9 solar masses. (4) NuSTAR's survey of the central Galaxy, several parsecs away from Sgr A, revealed a population of intermediate polars with a temperature of 20-40 keV. (5) The measurement of the X-ray background in the Galactic bulge indicates a population of dwarf novae with a characteristic emission temperature of 8 keV. These and other observations of the central part of the Galaxy will be presented in the talk.
Speaker: Roman Krivonos (Space Research Institute (IKI), Moscow, Russia) -
56
Magnetized white dwarf and its observational implications: Beyond the Chandrasekhar limit
Over the last one and half decades, along with my group members and collaborators, I have been exploring the possible existence of (highly) magnetized white dwarfs exceeding the Chandrasekhar limit. This helps understanding perculiar over-luminous type Ia supernovae which predict their progenitor mass well above 1.4 solar mass Chandrasekhar limit. By theory, numerical calculations and numerical simulations, we have been showing the possible existence and formation of stable super-Chandrasekhar white dwarfs, even from stellar evolutions. In this talk I will summarize the results and their multifold observational implications, including detecting by their gravitational wave emission by future missions.
The talk will be based on the following papers:
U. Das, B. Mukhopadhyay, Phys. Rev. Lett., 2013
S. Subramanian, B. Mukhopadhyay, MNRAS, 2015
B. Mukhopadhyay, A. R. Rao, JCAP, 2016
B. Mukhopadhyay, A. R. Rao, T. S. Bhatia, MNRAS, 2017
S. Kalita, B. Mukhopadhyay, MNRAS, 2019
A. Gupta, B. Mukhopadhyay, C. A. Tout, MNRAS, 2020
S. Kalita, T. Mondal, C. A. Tout, T. Bulik, B. Mukhopadhyay, MNRAS, 2021
M Bhattacharya, A. J. Hackett, A. Gupta, C. A. Tout, B. Mukhopadhyay, ApJ, 2022
D. Deb, B. Mukhopadhyay, F. Weber, ApJ, 2022Speaker: Prof. Banibrata Mukhopadhyay (Indian Institute of Science) -
16:30
Coffee break
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Weyl Incorporated Gravity and Galactic Halo Rotation
A modification of the Einstein-Hilbert Lagrangian by introducing an explicit coupling between the gravitational field, given by the Weyl tensor, and the matter-energy content, given by the stress-energy tensor, was proposed to explain flat galactic rotation curves without the exotic (non-baryonic) dark matter (DM) [Qadir, A., and Lee, H.W., IJMPD, 28, 2040014, (2019)], as Modified Relativistic Dynamics (MORD) and later called Weyl-Incorporated Gravity (WIG) [Qadir, A., Shahid, A., and Tahir, N., AJOM (accepted 2026)]. It was seen that a single value of the coupling constant $\lambda$ successfully explained the rotational velocities of eight edge-on spiral galaxies. Here we present a brief review of WIG and mention future prospects.
Speaker: Asghar Qadir (None) -
58
The no--hair theorems at work in M87*
Recently, a perturbative calculation to the first post--Newtonian order has shown that the analytically worked out Lense--Thirring precession of the orbital angular momentum of a test particle following a circular path around a massive spinning primary is able to explain the measured features of the jet precession of the supermassive black hole at the centre of the giant elliptical galaxy M87. It is shown that also the hole's mass quadrupole moment $Q_2$, as given by the no--hair theorems, has a dynamical effect which cannot be neglected, as, instead, done so far in the literature. New allowed regions for the hole's dimensionless spin parameter $a_*$ and the effective radius $r_0$ of the accretion disk, assumed tightly coupled with the jet, are obtained by including both the Lense--Thirring and the quadrupole effects in the dynamics of the effective test particle modeling the accretion disk. One obtains that, by numerically integrating the resulting averaged equations for the rates of change of the angles η and φ characterizing the orientation of the orbital angular momentum with $a_* = +0.98$ and $r_0=14.1$ gravitational radii, it is possible to reproduce, both quantitatively and qualitatively, the time series for them recently measured with the Very Long Baseline Interferometry technique. Instead, the resulting time series produced with $a_* = -0.95$ and $r_0=16$ gravitational radii turn out to be out of phase with respect to the observationally determined ones, while maintaining the same amplitudes.
Speaker: Lorenzo Iorio (MIM) -
59
Induced Wald Charge on Magnetized Kerr Black Hole
A rotating black hole immersed in an external uniform magnetic field acquires an induced electric charge — the Wald charge — through frame-dragging of the surrounding electromagnetic field. In this work we examine the formation of the Wald charge and its impact on the motion of charged particles near magnetized black holes. We combine an analytical treatment of the induced field structure with general-relativistic particle-in-cell simulations to capture the self-consistent plasma response.
Speaker: Martin Kološ (Institute of Physics, Silesian University in Opava) -
60
Electromagnetic field of charged axially-symmetric conductor with charge in the vicinity of Kerr black hole
The charged axially-symmetric conductor with charge in the vicinity of Kerr black hole is considered. The electromagnetic field of this conductor in the form of multipole expansion is calculated by using the Teukolsky equation. The structure of electric and magnetic field lines is analyzed. The case when conductor is located almost at the event horizon is considered. The astrophysical applications of the results are discussed.
Speaker: Stanislav Komarov (Belarusian State University) -
61
New Gravitational Instanton on a Warped Brane World Model
It is believed that black holes remain a clean laboratoryfor probing ideas about quantum gravity. Decades of work on these obscure objects have shown they behave could behave like ordinary thermodynamic systems with temperature and entropy, or to the extreme, even as elementary particles.
It remains a huge challenge to reconcile the large-scale properties with the underlying quantum description.We find a new exact time-dependent instanton solution on a vacuum Kerr-like warped spacetime in conformal dilaton gravity. Remarkably, the metric solution results from a first-order PDE, allowing the connection with self-duality. The solution can be described by a conformal K\"ahlerian manifold with Euclidean signature and a K\"ahler potential. As such, the self-dual nature makes the comparison with the Yang-Mills instanton counterpart solution interesting.
The antipodal boundary condition on the hypersurface of a Klein bottle $\sim \mathbb{C}^1\times\mathbb{C}^1$ is applied 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 bottle. The twist fits very well with the antipodal identification of the point on the horizon. No "cut and past" is necessary, so the Hawing particles remain pure without instantaneous information transport.
A local observer passing the horizon will not notice a central singularity in suitable coordinates.
The black hole paradoxes are also revisited in our new black hole model.
A connection is made with the geomeric quantization of $\mathbb{C}^1\times\mathbb{C}^1\sim S^3$, by considering the symplectic 2-form.
The model can be easily extended to the non-vacuum situation by including a scalar field. Both the dilaton and the scalar field can be treated as quantum fields when approaching the Planck area.Speaker: Dr Reinoud Slagter (ASFYON, Astronomisch Fysisch Onderzoek Nederland)
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Zeldovich as the Big Bang of Mind (public lecture)Speaker: Prof. Vladimir Lipunov (Lomonosov Moscow State University, SAI, Physics Department)
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Artificial Intelligence and cosmologyConvener: Yu Wang (ICRA/ICRANet/INAF)
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63
Gamma-Ray Bursts as probes of dark energy
Testing the $Λ$CDM model requires cosmological probes spanning the wide redshift interval between Type Ia Supernovae (SNe Ia, $z\lesssim2.9$) and the Cosmic Microwave Background (CMB, $z\approx1100$). Gamma-Ray Bursts (GRBs), observed up to redshift $z=9.2$, offer the opportunity to explore this regime. Here, we investigate how many GRBs are needed to become a useful cosmological probe capable of independently testing deviations from $Λ$CDM suggested by the recent DESI BAO observations. We develop forecasts based on the two-dimensional X-ray and optical Dainotti relations, between the luminosity at the end of the plateau phase and its rest-frame duration. Using simulated GRB samples constructed from the observed population, we evaluate the constraining power of GRBs on cosmological parameters within the $w$CDM and $w_0w_a$CDM models, both independently and in combination with CMB observations. Our results show that GRB samples containing several tens to hundreds of well-characterized plateau can already approach the precision currently achieved by CMB measurements on the Dark Energy (DE) equation-of-state parameter $w$. Particularly, a sample of $\sim66$ optical GRBs can reach a precision $σ_w \approx 0.47$, comparable to that obtained from Planck within the $w$CDM framework. Such sample sizes are already attainable through Machine Learning techniques that double the number of GRBs using inferred redshifts. These forecasts indicate that future GRB observations, when combined with next-generation transient missions and improved statistical techniques, will provide an independent high-redshift probe of cosmic expansion and will play an important role in testing the robustness of potential Dynamical DE signals suggested by other cosmological datasets
Speaker: Maria Dainotti (National Astronomical Observatory of Japan) -
64
Ranking Prompt–Plateau Correlations in Gamma-Ray Bursts with Symbolic Regression
Gamma-ray bursts (GRBs) show several empirical correlations that constrain their central engines, relativistic outflows, and radiation processes. One of the best known afterglow relations is the Dainotti anti-correlation between the X-ray plateau luminosity and the rest-frame plateau duration. Here we use symbolic regression to compare this relation with other low-dimensional correlations in the data. We first verify that symbolic regression can recover the Dainotti relation and then perform an unrestricted search for alternative analytical expressions. We find that correlations incorporating the prompt peak luminosity provide a better empirical description of the observations
than the classical two-parameter Dainotti relation, suggesting that the latter may be a projection of a more fundamental prompt–plateau relation.Speaker: Fatemeh Rastegar Nia (Alzahra university and ICRANet) -
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Revision and explaining SN 1054 by GRB 190114C and GRB 220101A
The Crab Nebula is the remnant of the high energy event occurred in 1054 AD and reported in several historical documents. Even if the chronology is not always coherent for several reasons (time distance from the event to the report, political censorship, religious re-framing of the event…) the correlation between a strong visible event in daytime and the sudden spread of plagues in Egypt and Constantinoples emerged, and the interpretation of the event as GRB fitted well all data available: the first strong half-hour of radiation was visible at the Eastern horizon in America, at the meridian in Europe/Egypt with the largest death toll, and only 18 hours after in China/Japan with exponentially reduced radiation (Ruffini and Sigismondi, 2024). The radiation of GRB 190114c extrapolated to 1000 years well represented the current radiation expressed by the Crab Nebula (visible radiation, X-rays and Gamma-rays).
The discovery of the 33 ms Crab Pulsar by Hewish and Bell in 1967 has been associated to a Supernova explosion which originated the whole Nebula, and this remained the prevailing “vulgata” of the Crab event up to 2024, even if a first interpretation as GRB was proposed in 2010 (Polcaro and Martocchia 2010) comparing the historically-deduced light curve with GRB 080319B, due to its extreme luminosity. In addition to the Nebula, the binary driven hypernova model of GRBs predicts the production of a condensed body (a ms Pulsar) and a Black Hole.
The GRB 220101A produced a newly formed millisecond-pulsar, strengthening the identification of the Crab Event with a GRB within the BDHN scenary.
The Black Hole responsible of the Gamma-rays radiation is within the Nebula, gravitationally bound to it.Speaker: Costantino Sigismondi (ICRA Sapienza and ICRANET Pescara) -
10:45
Coffee break
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Optical transients from non-explosive double white-dwarf mergers: the case of a central neutron star remnant
Discoveries of ultra-massive magnetic white dwarfs (WDs) and peculiar pulsars have been proposed to originate in double white dwarf (DWD) mergers. There are three possible post-merger central remnants of non-explosive mergers: 1) a stable sub-Chandrasekhar WD; 2) a rapidly rotating super-Chandrasekhar WD; 3) a neutron star (NS).
In this work, we explore the thermal transient arising from non-explosive DWD mergers that leave an NS remnant from the prompt collapse of the merged core. The transient is powered by the cooling of the expanding dynamical ejecta, with energy injection from magnetic dipole radiation, which depends on the dipole factor $D = B_d^2/P_0^4$, with $B_d$ and $P_0$ being the surface magnetic field strength and initial rotation period of the newborn NS. We simulate lightcurves in the Legacy Survey of Space and Time (LSST) bands and estimate the horizon and detection rates for these transients across a range of model parameters. We find LSST detection horizons upper limits ranging $30$--$820$ Mpc and corresponding detection rates $10^2$--$10^6$ yr$^{-1}$ for $\log D = 24$--$40$. Accounting for the survey cadence, we find that only configurations with $\log D = 36$--$40$ are detectable within $240$--$760$ Mpc, with detection rates $10^4$--$10^5$ yr$^{-1}$. Combined searches across surveys can compensate for the low cadence and improve the detection rates of fast and less energetic sources. Multi-wavelength campaigns can aid in detecting the spindown radiation at higher energies observable after the optical transient. Observations of these transients will provide direct evidence of the non-explosive DWD mergers, characterise the remnants and progenitor parameters, and the fraction of explosive and non-explosive mergers.Speaker: Ridha Fathima Mohideen Malik (Università degli Studi di Ferrara) -
67
Overview of the Euclid mission
The standard cosmological model successfully describes a wide range of observations, yet the nature of dark matter and dark energy remains unknown. Euclid is ESA’s space mission designed to address these questions by mapping the extragalactic sky with high-resolution optical imaging and near-infrared photometry and spectroscopy. Its main cosmological probes, weak gravitational lensing and galaxy clustering, will trace the growth of structure and the expansion history of the Universe across cosmic time. In this talk I will present an overview of the Euclid mission and highlight its most recent scientific results, from the first data releases to early demonstrations of Euclid’s capability to map the dark Universe.
Speaker: Mario Ballardini -
68
Cooling and emission of newborn quark stars
Cooling of newborn quark stars occurs through neutrino emission from their interiors and photon and electron-positron pairs emission from their surface. We will discuss the cooling process of bare hot quark stars with particular emphasis on luminosity and spectrum, providing input for ongoing observational programs in X-rays.
Speaker: Gregory Vereshchagin (ICRANet) -
69
On Synchrotron Radiation Within Non-homogeneous Astrophysical Radiator Paradigm
Numerous observations and numerical simulations show us that non-homogeneous magnetic fields are ubiquitous within astrophysical phenomena, be it in a regular or stochastic way. Nevertheless, models of astrophysical non-thermal radiation (namely synchrotron radiation) rarely address all the aspects of this matter. In this talk we will examine the limits of the standard synchrotron theory used in astrophysical settings and present certain preliminary ideas how to resolve them in practice. Also we will show how synchrotron theory itself indicates the presence of non-homogeneous magnetic fields with examples from the observations of radio supernovae and gamma ray bursts.
Speaker: Mile Karlica (Astronomical Observatory Belgrade)
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Gravity and cosmologyConvener: Manuel Hohmann (University of Tartu)
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70
On the formation of compact-object binaries from binary-driven hypernovae
I will present smoothed-particle hydrodynamics (SPH) simulations of the binary-driven hypernova (BdHN) scenario for long gamma-ray bursts (GRBs), focusing on the stability of the binary system during the supernova (SN) explosion. The progenitor of a BdHN consists of a carbon–oxygen (CO) star and a neutron-star (NS) companion. The core collapse of the CO star triggers an SN explosion and forms a newborn NS ($\nu$NS) at its center. Part of the SN ejecta is subsequently accreted by both the NS companion and the $\nu$NS.
BdHNe are classified into three subclasses according to the binary orbital period and the resulting accretion process. In BdHN I systems, characterized by compact orbits with periods of a few minutes, the NS companion reaches its critical mass and collapses into a black hole (BH), releasing about 1e52 erg. BdHN II systems have longer orbital periods, from tens of minutes to a few hours; the NS companion gains mass but remains stable, with an energy release of 1e50 - 1e52 erg. In BdHN III systems, with orbital periods of days, accretion is negligible and the released energy is of order 1e50 erg.
I will investigate whether the binary remains gravitationally bound after the SN explosion, leading to NS–BH systems in BdHN I and NS–NS systems in BdHN II and III, or whether the explosion disrupts the binary. The existence of bound remnants would support an evolutionary connection between the long- and short-GRB populations.Speaker: Dr Laura Marcela Becerra Bayona (Universidad Industrial de santander) -
71
Extreme Kerr-Newman Black Holes: Differential Geometry, Symmetry, and the Golden Ratio
Using the Christodoulou-Ruffini and Hawking mass-energy relations as a starting point, we investigate the properties of extreme black holes from a differential-geometry perspective. The geometry of black-hole horizons is of fundamental importance, as it offers deep insight into the structure of spacetime and the behavior of gravitating systems in the strong-field regime. We present two remarkable classes of extreme black holes in which the angular momentum and electric charge are related to the irreducible mass through either an irrational constant or the golden ratio.
In the first class, the fundamental physical quantities are connected to the irreducible mass by an irrational factor. A striking consequence is that the Gaussian curvature vanishes at the poles of the horizon, implying locally flat regions on the black-hole surface. This unusual and unexpected geometric property may significantly affect the propagation of particles and light near the polar caps.
In the second class, all physical quantities, including the irreducible mass itself, are governed by the golden ratio. This special symmetry gives rise to distinctive geometric structures and suggests intriguing connections between black-hole geometry, horizon topology, and fundamental mathematical constants.
These results are derived within Smarr’s differential-geometric framework, which also allows us to analyze, in a unified way, the hidden symmetries underlying the Schwarzschild, Kerr, and Reissner–Nordström solutions. Three representative cases corresponding to irreducible masses M=10 M_{Planck}, M=3 M⊙, and M=108 M⊙ are explicitly discussed. Particular attention is devoted to the structure and properties of the umbilic points of the horizon geometry.
Finally, we estimate the extractable energy of extreme Kerr–Newman black holes through reversible and irreversible transformations, distinguishing between families of horizons that can be globally embedded in Euclidean space (E3) and those requiring pseudo-Euclidean embeddings.Speaker: Prof. Giorgio SONNINO (International SOLVAY Institutes for Physics and Chemistry & Université Libre de Bruxelles (U.L.B.)) -
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Non-Keplerian Galaxy Rotation Curves as a Testing Ground for Precanonical Quantum Gravity
We show that a variety of non-Keplerian galaxy rotation curves, together with the corresponding modifications of the Newtonian potential and dynamics, including MOND, qMOND, and mMOND-type behaviors, can be derived for test particles propagating on a background quantum geometry associated with a quantum spin connection, as described by precanonical quantum gravity (pQG).
In particular, we identify a quantum gravitational origin of Milgromian dynamics and derive a relation between the Milgromian acceleration scale $a_0$ and the cosmological constant. Both quantities are expressed in terms of the variance of the distribution of spin-connection components determined by the quantum gravitational wave function within pQG. Their smallness is traced back to the precanonical quantization scale $\varkappa$, which enters the formulation of precanonically quantized Einstein--Yang--Mills theory and appears in estimates of the mass gap in quantum Yang--Mills theory. The resulting expression for the cosmological constant is reminiscent of the formula proposed by Zeldovich in 1967.
These results suggest that pQG provides a first-principles framework for describing the very weak-field regime of galactic dynamics, offering a theoretically motivated alternative to phenomenological dark matter models and modified gravity scenarios.
Based on: Y.B. Zel'dovich, JETP Lett. 6 (1967) 316; I. Kanatchikov et al., arXiv:1212.6963, 1512.09137, 1706.01766, 2308.08738, 2311.05525; IJGMMP 14 (2017) 1750123; J. Phys.: Conf. Ser. 3017 (2025) 012031; EPL 150 (2025) 59002; Mod Phys Lett A 2541012 (2025); and work in progress (with V.A. Kholodnyi, J. Kozicki, and M.E. Pietrzyk).
Speaker: Dr Igor Kanatchikov (Natl. Quantum Information Center in Gdansk) -
16:30
Coffee break
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Evolution of Virial Clouds -- II: From the formation of first stars up to their explosion
It had been proposed [Qadir A., Tahir N., and Sakhi M., PRD 100, (2019)] that virial clouds “propped up” by the cosmic microwave background (CMB), and hence at that temperature, populate dark matter halos and may account for a significant fraction of the missing baryons. To understand the nature of these clouds, it is necessary to trace their evolution from the last scattering surface (LSS) at $z=1100$ to the present day. The first stage of this evolution, spanning the redshift range $1100 \geq z \geq 48$, was investigated in [Tahir, N., Qadir, A., Sakhi, M., and De Palois, F., EPJC, 81, 827 (2021)]. In the present work, we study the second stage of their evolution, from the formation of the first generation of stars $(z = 48)$ up to the epoch of their supernova explosions $(z = 10)$.
Speaker: Noraiz Tahir (Department of Physics and Astronomy, School of Natural Sciences (SNS), National University of Science and Technology (NUST), H12, Islamabad, Pakistan) -
74
Neutrino Mixing in Torsionful Spacetimes: Quantum-Gravity Signatures and Dark-Universe Implications
Spacetime torsion provides a natural bridge between spin, gravity and quantum fields, and may leave observable imprints in fermionic sectors relevant to cosmology. I will discuss recent results on neutrino mixing in torsionful spacetimes within a quantum-field-theoretical framework, focusing on the phenomenological aspects most directly connected with relativistic astrophysics, quantum gravity and the dark Universe.
In the Einstein–Cartan framework, both constant and linearly time-dependent torsion backgrounds modify the energy spectrum of mixed neutrinos. This leads to spin-orientation-dependent oscillation formulae, shifts in oscillation amplitudes and frequencies and corrections to CP-asymmetry. These effects become especially relevant when the torsion scale is comparable to neutrino masses and in the very-low-momentum regime, suggesting relic or non-relativistic neutrinos as promising probes of torsion-induced physics.
I will then connect these microscopic signatures with broader cosmological questions, discussing how torsionful fermionic vacua and flavor condensates may affect the energy-momentum tensor, back-reaction mechanisms and possible dark-sector phenomenology. Finally, I will outline potential indirect tests through future low-energy neutrino-capture experiments, such as PTOLEMY and argue that torsion-induced modifications of neutrino mixing can provide a complementary window on physics beyond standard general relativity.
Speaker: Simone Monda (Università degli Studi di Salerno) -
75
Towards an Action Principle Unifying the Standard Model and Gravity
A single geometric invariant fixes the relative normalization and structure of gravity, Yang-Mills theory, and fermion kinetic terms, including ghost freedom in the gravitational sector, without tuning. Our results establish a minimal geometric route to unification that does not rely on extra dimensions or symmetry breaking by hand. Unlike previous gauge-gravity constructions, the relative normalizations and ghost freedom emerge from a single Clifford-algebraic invariant, without explicit symmetry breaking.
Speaker: Fernando Izaurieta (Universidad San Sebastián) -
76
Addressing the Hubble tension with a dynamical Λ(z) induced by galactic gravitational self-energy and by backreaction force from gas cloud collapse
In a recent publication, we derived a general relativity (RG) gauge-invariant solution modelling a granular universe composed of spherical bodies with a radial Gaussian density profile. In this framework, a cosmological constant Λ emerges natively from the gravitational self-energy of these discrete nodes. Energy conservation dictates a uniform compactness ratio M/σ^2 across all bodies, a relation closely met by the elliptical galaxies as shown in the GAMA survey. This setup yields: Λ≈1/(12 π^3) (κ a c^2 M/ σ^2)^2 which, using the compactness measured in the GAMA survey, evaluates to Λ≈0.9 x 10^-52 m^-2, a value close to modern observations. The model predicts the R = k (1+z)^-1.5 size scaling confirmed by the 3D-HST+CANDELS survey and, unlike standard ΛCDM theory, the model preserves total energy conservation.
Before gas clouds collapsing around z≈3 the universe was mostly homogeneous resulting in this model to Λ≈0. During the Lyman-α forest epoch an intense gas clouds collapsing into stars and black holes occurred. We extended our RG model to purely radial collapsing nodes which gave (κa^2/4 π^3 R^2) M d^2R/dt^2 < 0 . This backreaction force of the gas cloud collapse reached a peak around z≈2 , and later declined around z≈1.5 when massive galaxies ran out of cold gas or experienced quenching shutting down their star formation. At this epoch, the galaxies began their assembling into their modern structures, raising the cosmological constant to its current baseline value.
Integrating this dynamical Λ(z), while targeting the current Hubble parameter of H0 = 73 km/s/Mpc , yields a perfect validation against the Planck cosmic microwave background angular scale θ*=0.010410 and the latest DESI BAO data. Notably, the model predicts a structure clustering amplitude of S8≈0.81 in line with the BOSS/DESI Deep Scale Galaxy Clustering data survey. The proposed model successfully bypasses the need for an unexplained, speculative dark energy burst.Speaker: Stephan Walrand (université catholique de Louvain) -
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Concluding remarksSpeaker: Remo Ruffini (ICRANet, ICRA, INAF)
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