The electron Born self-energy (eBse) model assumes a finite-sized electron of radius R_e = 1.9 x 10^-20m, determined from electron–positron collisions at LEP. The Born self-energy U_e^B, corresponding to the energy contained in the surrounding electric field, provides a quantitative description of Dark Energy (Astrophys Space Sci 365, 64 (2020); Phys Sci Forum 2, 9 (2021)). Specifically, this model explains (i) the magnitude of DE, (ii) the occurrence of a deceleration-acceleration transition at a redshift z ~ 0.8, and (iii) possesses an equation of state w = -1. (In Quantum Electrodynamics the electron is assumed to be a point particle (R_e = 0), thus, U_e^B ~ 1/R_e is divergent and is “renormalized away” by assuming that U_e^B is contained within the electron rest mass m_e.) w = -1 implies that two electron Born masses m_e^B = U_e^B/c² will experience a gravitational repulsion, whereas, m_e^B and an uncharged mass will experience the normal gravitational attraction. m_e^B (~ 40 m_p) is a Dark Matter candidate which provides a good description of the Grand Rotation Curves for the Milky Way and M31 galaxies out to distances of ~ 400 kpc (Sci Rep 14, 24090 (2024)). (The difference between DE and DM, in this model, is as follows: DE arises from the time-dependent creation of m_e^B in intergalactic space due to ionization of hydrogen, whereas, DM is a time-independent effect arising from the presence of a halo of electrons, along with their associated m_e^B, that surrounds a galaxy.) Early in the Universe’s expansion history, for electrons and positrons of finite-size, a glass transition occurs at a maximum number density of ~ 1/(2R_e)³ corresponding to physical contact between particles. This glass transition possesses properties akin to Cosmic Inflation (Sci Rep 13, 21798 (2023)). A brief summary of the eBse model and its interconnections to DE, DM, and CI will be provided in this contribution.

The cosmological redshift drift (Sandage–Loeb effect) offers a unique, model-independent probe of the expansion of the Universe, by directly measuring the temporal fluctuation of cosmic redshift. In this study, we examine the viability of employing the Square Kilometre Array (SKA) to detect the redshift drift signal using neutral hydrogen (HI) 21 cm emission from galaxies and 21 cm absorption from Damped Lyman-α systems. We demonstrate how, by focusing on ultra-high spectral resolutions of 0.001–0.002 Hz and a semi-annual observational baseline, predicted SKA data spanning the redshift range 0 < z < 1 may attain millimeter-per-second sensitivity to the velocity drift. Simulations show that in samples of more than a billion HI-emitting galaxies, velocity drifts can be restricted at the level of 0.05–0.15 cm s⁻¹ every 0.5 yr, whereas HI absorption systems provide complementary but weaker constraints due to their lower number density. Using simulated redshift drift data, we constrain cosmological parameters for a number of dark energy models, resulting in Hubble constant and matter density values that are consistent with existing observations and dark energy equation-of-state parameters close to a cosmological constant. Our findings highlight the ability of SKA HI 21 cm data to directly investigate cosmic acceleration at low redshift, offering a compelling and independent test of dark energy to supplement optical redshift drift investigations at higher redshifts.

Third-generation gravitational-wave observatories such as the Einstein Telescope (ET) will enable unprecedented studies of both cosmology and compact-object populations using large samples of “dark sirens,” i.e., gravitational-wave events without electromagnetic counterparts. In this presentation, we explore the ability of ET to jointly infer the underlying cosmological model and the mass and redshift distributions of binary black hole (BBH) mergers using one year of observations. We assume a flat ΛCDM cosmology and model the BBH population with a smoothed power-law plus Gaussian mass distribution and a Madau–Dickinson parametrization for the merger-rate redshift evolution. Using mock BBH catalogs generated for different signal-to-noise ratio (SNR) detection thresholds, we perform a hierarchical Bayesian analysis that consistently accounts for selection effects and measurement uncertainties. We find that decreasing the SNR threshold leads to a substantial improvement in the precision of the Hubble constant H₀ and the matter density parameter Ωₘ,₀, primarily due to the inclusion of a larger number of high-redshift events. However, this gain is accompanied by non-trivial degeneracies between cosmological and astrophysical parameters, whose structure evolves with the SNR threshold. This study highlights the importance of joint population–cosmology inference with third-generation detectors and demonstrates the strong potential of the Einstein Telescope to advance dark-siren cosmology while simultaneously deepening our understanding of black hole formation and evolution.

We investigate the implications provided by the modified Painleve–Gullstrand coordinates in the context of quintessence for the Kiselev black hole. In this regard, we set up a fully static line element in terms of lapse and shift functions, while also including the deformation parameter, which signals deviation from the standard Painleve–Gullstrand metric. We address two specific issues related to the problems of radiation and dust, as furnished by the corresponding barotropic index parameter, and study the related consequences by performing a range of analyses to explore the influence imposed by quintessence. We perform a thermodynamical analysis of our results by determining the Hawking temperature and entropy for the cases of radiation and dust. The results are obtained in closed form and show their sensitivity to quintessence. We set up a framework wherein we compare the effect of the deformation parameter on the velocity of an infalling particle. We analyze and comment on the dependence of the quintessence parameter on the mass and charge of the Kiselev black hole. We show explicitly the entropy behaviour for the radiation and dust cases in the plots made with respect to the variation in black hole mass M and black hole charge Q for the quintessence parameter \alpha.

As was shown by Ellis in gr-qc/0411096, one can establish a correspondence between the Schwarzschild metric and a warp drive-type metric, making it possible to consider a warp drive in a black hole background. We elaborate upon this result and demonstrate that the black hole’s gravitational field can alleviate the violations of energy conditions, reducing the amount of negative energy required to sustain a warp bubble. Besides, we demonstrate that the black hole horizon is effectively absent for the observers inside the bubble, making it possible for them to send a light signal from the inside to the outside; however, the front wall of the warp bubble would emit Hawking radiation, possibly making the bubble unstable. The warp bubble would also possibly increase the black hole's entropy.

We also generalize the Ellis scheme to the case of Morris-Thorne wormholes and prove that Alcubierre warp drives cannot traverse humanly traversable wormholes and can only pass through those that either have a horizon or violate the flare-out condition. In addition, we consider warp drives in a de Sitter universe, and demonstrate that in this case, it's possible to interpret the warp bubble just as rearrangement of vacuum energy, in contract to exotic "negative energy". We discuss the implications of our results.

Transient noise artifacts, or glitches, pose a serious challenge for gravitational-wave astronomy. These artifacts can overlap with real gravitational-wave signals and lead to inaccurate parameter estimation. As existing detectors are upgraded and new detectors come online, the ability to accurately identify and classify glitches will become increasingly important. While there are existing methods for handling glitches, many are computationally expensive, and as data volumes grow, the cost of removing or mitigating these glitches increases significantly.

This motivates the following question: can machine learning serve as an effective tool for glitch classification and mitigation? Using labeled data from Gravity Spy, we expand and balance our dataset using generative adversarial networks (GANs). We then evaluate a variety of convolutional neural networks (CNNs) and vision transformer architectures to assess their performance in classifying gravitational-wave glitches. Hyperparameters such as learning rate and weight decay are optimized using Optuna to achieve optimal performance. Model performance is evaluated using standard classification metrics, including accuracy, precision, recall, F1 score, and confusion matrices.

By comparing a diverse set of models, we examine the trade-offs between model complexity, interpretability, and classification performance. These results provide guidance for selecting appropriate machine learning models for future gravitational-wave detector characterization pipelines, while doing so at a computationally affordable cost.

Einstein General Relativity Theory is usually used for the interpretation of the experimental cosmological data in the Friedman-Robertso-Worker framework. Meanwhile, the General Relativity Theory is verified only in the Solar system and in the near cosmological environments.

Observations of the black hole images open the unique possibility for this verification in the strong field limit when Newtonian gravitational potential is of the squared light velocity order and when gravitation dominates over astrophysical factors.

Experimental verification of the Einstein General Relativity Theory and different Modified Gravity theory by observations of detailed images of supermassive black holes with the use of projected Space Millimetron Observatory with nano-arcsecond angular resolution. These observations are very crucial for physical interpretation of astrophysical and cosmological data on the Universe and for understanding, in part, the physical origin of enigmatic dark matter and dark energy. Scrutinizing the different gravity theories would be possible in the nearest future after construction of the Space Millimetron Observatory with nano-arcsecond angular resolution.

The very promising astrophysical supermassive black holes for these verifications are the SgrA* at the center of our native Milky Way Galaxy and supermassive black hole M87* at the center of the giant elliptical galaxy M87, which itself is placed in the Virgo galactic cluster. The fist images of these black holes were observed recently by the Event Horizon Telescope collaboration with milli-arcsecond resolution.

It must be accented that the explicit point of this research is the verification of Einstein General Relativity and different modifications of gravity theory in the strong field limit.

In this paper, we present a detailed investigation of two-fluid cosmological models formulated within the anisotropic Bianchi type I spacetime. The framework considers the universe to be filled with two distinct components: a standard barotropic fluid representing ordinary matter and radiation and a dark energy component introduced to account for the late-time accelerated expansion of the universe. Both interacting and non-interacting scenarios between the two fluids are examined, allowing us to assess how the exchange or absence of energy–momentum transfer influences the overall cosmological dynamics.

Einstein field equations are solved explicitly for each case, and the evolution of key physical and geometrical parameters—such as directional Hubble rates, expansion scalar, shear scalar, and the density parameters—is analyzed with reference to recent observational data. Our results indicate that the proposed models are most accurately described by quintessence-type dark energy, exhibiting behavior consistent with a dynamically evolving equation of state. A significant outcome of the analysis is that the total density parameter Ω remains invariant irrespective of whether the fluids interact, underscoring the robustness of the model.

Furthermore, the asymptotic behavior of the cosmological parameters aligns with the predictions of the standard ΛCDM model. In particular, we demonstrate that the deceleration parameter approaches q→ −1 and the jerk parameter tends to j(t)→1 as cosmic time t→∞, indicating a smooth approach toward a de Sitter phase. These outcomes suggest that the constructed two-fluid Bianchi type I models provide a viable theoretical framework compatible with current cosmological observations.

The main objective of this talk is to identify black hole solutions that satisfy the third law of thermodynamics. We begin by examining the possibility of finding such solutions within the Einstein–Maxwell–Dilaton models with purely electric, purely magnetic, and electric–magnetic configurations coupled through two independent exponential coupling functions and subsequently analyze their thermodynamic properties. Our primary focus will be on anisotropic Lifshitz and hyperscaling Lifshitz solutions. It was found that for this model, the third law of thermodynamics is valid, while for most ordinary black holes, such as Schwarzschild, rotating, and charged black hole solutions, the third law of thermodynamics is violated.

We establish a duality between the Bose gas and these black brane solutions. This duality provides a statistical description of black hole entropy for various dimensions and anisotropy parameters. Our framework enables the construction of a microscopic statistical description of entropy for a broad class of non-extremal black holes through a generalization of the holographic duality approach. We demonstrate that anisotropy parameters serve as natural regulators of black hole/Bose gas duality.

The first part of the talk is based on the joint paper, "Black brane/Bose gas duality and the third law of thermodynamics", Irina Aref'eva, Igor Volovich, Daniil Stepanenko , 2411.01778 [hep-th], published in Teor.Mat.Fiz. 222 (2025) 2, 276-284, Theor.Math.Phys. 222 (2025) 2, 276-284.

In bouncing cosmological models, either classical or quantum, the Big Bang singularity is replaced by a regular bounce. A challenging question in such models is how to keep the shear under control in the contracting phase, as it is well-known that the shear grows as fast as 1/a⁶ toward the bounce, where a is the expansion factor of the universe. A common approach is to introduce a scalar field with an ekpyrotic-like potential, which becomes negative near the bounce, so the effective equation of state of the scalar field will be greater than one, whereby it dominates the shear and other matter fields in the bounce region. As a result, a homogeneous and isotropic universe can be produced. In this paper, we study how the ekpyrotic mechanism affects the inflationary phase in both loop quantum cosmology (LQC) and a modified loop quantum cosmological model (mLQC-I) because in these frameworks, the inflation is generic without such a mechanism. After numerically studying various cases in which the potential of the inflaton consists of two parts, an inflationary potential and an ekpyrotic-like one, we find that, despite the fact that the influence is significant, by properly choosing the free parameters involved in the models, the ekpyrotic-like potential dominates in the bounce region, during which the effective equation of state is larger than one, so the shear problem is resolved. As the time continuously increases after the bounce, the inflationary potential grows and ultimately becomes dominant, resulting in an inflationary phase. This phase can last long enough to solve the cosmological problems existing in the Big Bang model.