arXiv subjects

V. G. Gurzadyan

Publications and source records attributed to V. G. Gurzadyan.

At least 19 recordsLinked to original sources

arXiv2026

The stability of voids in the Local Universe: The role of the cosmological constant

The Vlasov kinetic formalism is employed to study the evolution and stability of cosmic voids in the Local Universe, taking into account not only the gravitational attraction, but also the repulsive effect of the cosmological constant (i.e., local dark energy). In accordance with the theorem on the general function of the identity between the gravitational fields of a sphere and a point mass, the cosmological constant provides a natural explanation for the Hubble tension, attributing it to local and global flows characterized by different Hubble parameters. The crucial role of the Λ-repulsion in maintaining the stability of voids at the present epoch is demonstrated when Landau damping suppresses discrete collapse modes and prevents random local density perturbations inside the voids from growing and incorporating new galaxies into the walls. Inside the voids, the Λ-repulsion exceeds the attractive force of the residual matter, driving matter outward and accelerating its migration toward the void boundaries. In the Local (late) Universe, cosmic voids have entered a stage characterized by stable and more pronounced walls, as studied via observational surveys across different redshift ranges.

astro-ph.CO↗

arXiv2026

Disk-like galaxies at 4 < z < 7.7 : JWST/NIRCam morphologies revealed by denoising VAE-GCNN classification

Understanding the prevalence of disk-like galaxies at very high redshifts is crucial for constraining the early formation of angular momentum-supported structures. The advent of JWST now permits rest-frame UV and optical morphological studies deep into cosmic epochs where disks have traditionally been considered uncommon. We apply an identical denoising VAE-GCNN classification pipeline to multi-filter JWST/NIRCam cutouts in order to obtain homogeneous, morphology-based disk fractions across the sample. Our approach comprises two steps: (i) a U-Net Variational Autoencoder (VAE) is trained to remove astrophysical and instrumental contaminants while preserving intrinsic morphology, and (ii) a rotation - and reflection - equivariant GCNN classifier is applied to the denoised cutouts to distinguish disk-like galaxies from non-disks. We determine the fraction of disk-like galaxies as 0.34 for a sample of JWST 100 galaxies over the redshift range 4 < z < 7.7, also in dependence on the galaxy mass range. Our GCNN-based morphological analysis indicates that disk-like systems constitute a significant fraction of the considered high-redshift population and underscore the importance of such studies for the models of disk formation in the first billion years.

astro-ph.GA↗

arXiv2026

Kolmogorov analysis of pulsar TOA

The Kolmogorov stochasticity parameter (KSP) as a sensitive descriptor of the degree of randomness of signals was used to analyze the properties of the NANOGrav pulsar timing data associated with a stochastic gravitational wave background. The time of arrival (TOA) data of white noise for 68 pulsars were analyzed regarding their KSP properties. The analysis enabled us to obtain the degree of randomness of the white noise for various pulsars and to reveal its inhomogeneity, i.e., pulsars with low and high randomness of the white noise. The time dependence of the randomness in the white noise was also studied, indicating the existence of nonstationary physical processes influencing the pulsar timing. The KSP is thus acting as an indicator for the degree of the agreement between the observations and the timing models and as a test in revealing the contribution of various physical processes in the stochastic background signal.

astro-ph.IM↗

arXiv2025

Cosmic voids and the kinetic analysis. V. Hubble tension, the cosmological constant and aperiodic filaments

We study the appearance and specific properties of the structures in the local Universe by means of the Vlasov kinetic technique. We consider the role of the cosmological constant in local structure formation via the theorem on the general function that satisfies the identity of the gravity of the sphere and of the point mass. Then, the Hubble tension is naturally explained as a result of two flows, a local and a global one, with non-coinciding Hubble parameters. The linearized Vlasov-Poisson equation with the cosmological term is shown to lead to van Kampen's waves, Landau damping, and then to aperiodic structures. Aperiodicity thereby emerges as a intrinsic feature of the filamentary and void structure of the local Universe, and reveals the self-consistent field mechanism of its formation. The damping of the aperiodicity is then predicted and can be observationally traced upon the increase in the scale of the filaments.

astro-ph.CO↗

arXiv2025

Focus Point on Tensions in Cosmology from Early to Late Universe: Part II: New Directions in the Light of Observations from the Most Modern Astronomical Facilities

The papers included in this Focus Point collection are devoted to the studies on the cosmological tensions and challenges stimulated by the latest observational data. The first results of the LARES-2 laser ranging satellite on the high precision testing of the frame-dragging effect predicted by General Relativity are presented. The data on the S-stars monitoring in the Galactic center obtained by GRAVITY collaboration were analysed within the Physics-informed neural network (PINN) approach. The results enabled to probe the role of the cosmological constant, of the dark matter, the star cluster in the core of the Galaxy obtaining an upper limit for the star density. The topics include the conversion of high-frequency relic gravitational waves into photons in cosmological magnetic field, cosmological gravitational waves stochastic background generation through the spontaneous breaking of a global baryon number symmetry, observational predictions of the Starobinsky inflation model and other studies.

astro-ph.CO↗

arXiv2025

On the Earth's tidal perturbations. II. LARES 2 satellite

Laser-ranging satellites have proved their efficiency in high precision testing of General Relativity and constraining modified gravity theories proposed to explain the dark sector and the cosmological tensions. The LARES 2 satellite launched in 2022, is currently providing improved information regarding the frame-dragging effect predicted by General Relativity, as well as the geodesy, thus essentially complementing the data of already existing laser-ranging satellites. The proper knowledge of the Earth's tidal perturbation modes is essential for accurately extracting the sought frame-dragging signal. We present the results of computation of 110 significant modes in Doodson number classification for the parameters of LARES 2 satellite, continuing our previous study on those obtained for the LARES satellite.

gr-qc↗

arXiv2025

Kolmogorov analysis of JWST deep survey galaxies

JWST galaxy deep spectral surveys provide a unique opportunity to trace a broad range of evolutionary features of galaxies and the intergalactic medium given the huge distance the photons are propagating. We have analyzed the spectral data of JWST galaxies up to a redshift of around 7 using the Kolmogorov technique, which is an efficient tool for testing the tiny comparative randomness properties of cumulative signals, that is, for distinguishing the contributions of regular and stochastic sub-signals. Our aim is to determine if certain identical spectral features of galaxies have undergone any distortions or systematic evolution across a broad range of redshifts. Our results indicate a change in the spectral properties of the sample galaxies at around z \simeq 2.7 at over a 99% confidence level.

astro-ph.GA↗

arXiv2025

Structure formation in the local Universe and the cosmological constant

The structure formation in the local Universe is considered within the weak-field modification of General Relativity involving the cosmological constant. This approach enables to describe the dynamics of groups and clusters of galaxies, to explain the discrepancy in the observational properties of the local (late) and the global (early) Universe, i.e. the Hubble tension as a result of two flows, local and global ones, with non-equal Hubble parameters. The kinetic analysis with the modified gravitational potential involving the cosmological constant is shown to predict semi-periodical structure of filaments in the local universe. In the local scale this complements the Zeldovich pancake theory of evolution of the primordial density perturbations and of structure formation in the cosmological scale. The role of the cosmological constant is outlined in rescaling of the physical constants from one aeon to another within the Conformal Cyclic Cosmology.

gr-qc↗

arXiv2025

Cosmic voids and the kinetic analysis. IV. Hubble tension and the cosmological constant

The formation of the cosmic structures in the late Universe is considered using Vlasov kinetic approach. The crucial point is the use of the gravitational potential with repulsive term of the cosmological constant which provides a solution to the Hubble tension, that is the Hubble parameter for the late Universe has to differ from its global cosmological value. This also provides a mechanism of formation of stationary semi-periodic gravitating structures of voids and walls, so that the cosmological constant has a role of the scaling and hence can be compared with the observational data for given regions. The considered mechanism of the structure formation in late cosmological epoch then is succeeding the epoch described by the evolution of primordial density fluctuations.

gr-qc↗

arXiv2025

Messier 90 galactic halo rotation in the microwaves

We used Planck data to study the Virgo Cluster's galaxy M 90 and its surroundings. We find, as in the case of certain galaxies of the Local Group and its vicinity, a substantial temperature asymmetry that probably arises from the rotation of the M 90 halo and extends up to about one degree from its centre. This temperature asymmetry is particularly remarkable as M 90 is a rare blueshifted galaxy of the Virgo Cluster, and it thus has possible implications for the cluster internal dynamics versus the galactic halo's formation and structure. Possible explanations for the observed effect are discussed.

astro-ph.GA↗

arXiv2024

The Supernova of 1054AD, the Armenian chronicle of Hetum, and Cronaca Rampona

The rareness of nearby supernovae ensures particular value to the historic records for determination of their light curves. We provide the translation of 13th century Armenian chronicle of Hetum, which by its unexpected association to Cronaca Rampona and other chronicles can influence the debates whether there are reliable European records of the supernova of 1054 AD, as well as the analysis of the records vs the conjunction with the Moon and their role in assigning of the Type I or II to that supernova.

physics.hist-ph↗

arXiv2024

S2-star dynamics probing the Galaxy core cluster

The star cluster surrounding the supermassive black hole in the center of Milky Way is probed using the data on the S2 star. The value of precession found at the physics-informed neural networks (PINN) analysis of the S2 data is used to consider the role of the scattering of S2 star on stars of the cluster, described by a random force given by the Holtsmark distribution. The critical value for the star density of the core cluster for which the observed precession value by PINN lies inside 70% confidence interval (between 15% and 85% quantiles) around the median of precession due to scattering, is obtained as n_crit \approx 8.3 10^6 pc^-3, that is at higher star densities the perturbation of the orbit of S2 would exceed the observed one.

astro-ph.GA↗

arXiv2024

Smearing of primordial gravitational waves

A mechanism for smearing of the primordial gravitational waves during the radiation-dominated phase of the evolution of the Universe is considered. It is shown that the primordial gravitational waves can possess hyperbolicity features due to their propagation through the matter inhomogeneities. This mechanism of smearing can lead to the flattening of the original gravitational wave spectrum and hence has to be taken into account at the interpretation of the properties of primordial gravitational background on the detection of which are oriented ongoing and forthcoming experimental facilities.

gr-qc↗

arXiv2024

Neural Network Analysis of S2-Star Dynamics: Extended mass

Physics-informed neural network (PINN) analysis of the dynamics of S-stars in the vicinity of the supermassive black hole in the Galactic center is performed within General Relativity treatment. The aim is to reveal the role of possible extended mass (dark matter) configuration in the dynamics of the S-stars, in addition to the dominating central black hole's mass. The PINN training fails to detect the extended mass perturbation in the observational data for S2 star within the existing data accuracy, and the precession constraint indicates no signature of extended mass up to 0.01% of the central mass inside the apocenter of S2. Neural networks analysis thus confirm its efficiency in the analysis of the S-star dynamics.

gr-qc↗

arXiv2023

Neural Network Analysis of S-Star Dynamics: Implications for Modified Gravity

We studied the dynamics of S-stars in the Galactic center using the physics-informed neural networks. The neural networks are considered for both, Keplerian and the General Relativity dynamics, the orbital parameters for stars S1, S2, S9, S13, S31, and S54 are obtained and the regression problem is solved. It is shown that the neural network is able to detect the Schwarzschild precession for S2 star, while the regressed part revealed an additional precession. Attributing the latter to a possible contribution of a modified gravity, we obtain a constraint for the weak-field modified General Relativity involving the cosmological constant which also deals with the Hubble tension. Our analysis shows the efficiency of neural networks in revealing the S-star dynamics and the prospects upon the increase of the amount and the accuracy of the observational data.

physics.gen-ph↗

arXiv2023

Cosmic voids and the kinetic analysis. III. Hubble tension and structure formation in the late Universe

We study structure formation in the late Universe within the Vlasov kinetic self-consistent field approach. Our work is principally focused on the use of the modified gravitational potential with a repulsive term of the cosmological constant, which is directly linked to observations that enable characterizations of the Hubble tension as the result of local and global flows. We formulate the criteria for the formation of the semi-periodic gravitating structures, along with the predictions of their quantitative scales associated with observable parameters. Our principal conclusion is that filament formation in the Local (late) Universe can proceed as a deterministic process that is distinct from the structures at larger scales that result from the essentially stochastic dynamics of density perturbations.

astro-ph.CO↗

arXiv2023

Cosmic voids and the kinetic analysis. II. Link to Hubble tension

We consider a principal problem, that of the possible dominating role of self-consistent gravitational interaction in the formation of cosmic structures: voids and their walls in the local Universe. It is in the context of the Hubble tension as a possible indication of the difference in the descriptions of the late (local) and early (global) Universe. The kinetic Vlasov treatment enables us to consider the evolution of gravitating structures where the fundamental role has the modified gravitational potential with a cosmological constant, leading to the prediction of a local flow with a Hubble parameter that is nonidentical to that of the global Hubble flow. The Poisson equation for a potential with an additional repulsive term, including an integral equation formulation, is analyzed, and we predict the appearance of multiply connected two-dimensional gravitating structures and voids in the local Universe. The obvious consequence of the developed mechanism is that the cosmological constant poses a natural scaling for the voids, along with the physical parameters of their local environment, which can be traced in observational surveys.

astro-ph.CO↗

arXiv2022

Gravitational waves as waveguides

We show that gravitational waves can act as waveguides for electromagnetic radiation, that is if the latter is initially aligned with the gravitational waves, then the alignment will survive during the propagation. The analysis is performed using the Hamiltonian formalism and the Jacobi equation for null geodesics and conditions for certain cases of polarization of the waves are obtained. The effect of waveguiding by the gravitational waves can influence the interpretation of associated gravitational and electromagnetic wave events, since the latter cannot necessarily obey the inverse square decay law for intensity.

gr-qc↗