arXiv subjects

I. V. Fomin

Publications and source records attributed to I. V. Fomin.

14 recordsLinked to original sources

arXiv2026

Corrections to inflationary models induced by non-minimal coupling between scalar field and curvature

In this paper, we consider possible corrections to the characteristics of inflationary models based on a specific parametrization of the non-minimal coupling between the scalar field and curvature. At the inflationary stage, these corrections lead to a deformation of the scalar field potential and a corresponding deviation in the determination of the cosmological perturbation parameters. At the same time, it is shown that the proposed parametrization yields a description of the reheating stage dynamics completely analogous to the case of Einstein gravity with minimal coupling between the scalar field and curvature. For a model-independent analysis of inflationary corrections induced by a non-minimal coupling, a classification of inflationary scenarios based on the expansion in series of the dependence of the tensor-to-scalar ratio on the spectral index of scalar perturbations is considered. It is also shown that this approach allows for the inclusion of well-known inflationary models as special cases.

gr-qc↗

arXiv2026

Low-frequency gravitational waves coupled with electromagnetic waves in material media

The influence of the low-frequency gravitational waves coupled with electromagnetic waves in material media on the test masses is investigated. The propagation of coupled gravitational waves in rarefied gases and cold magnetized plasma is considered. It has been shown that under specific conditions the amplitude of the coupled gravitational waves in a media reaches values of the order of the amplitude of transverse gravitational waves from external astrophysical sources. The specific properties of longitudinal gravitational waves coupled with electromagnetic waves in a medium in relation to transverse gravitational waves from external sources are considered as well.

gr-qc↗

arXiv2025

Seed models in scalar field cosmology

The correspondence of single-field cosmological models based on Einstein gravity to modern observational data is considered. A method is proposed to determine possible types of dynamics based on extreme values of the scalar field. It is shown that within the framework of this approach, it is possible to obtain a limited class of known inflationary models at early times. It is also shown that on large times the proposed approach leads to the $Λ$CDM--model in order to describe the dynamics of the second accelerated expansion of the universe. An interpretation of the considered models is presented as a starting point for constructing verifiable cosmological models based on modified gravity theories.

gr-qc↗

arXiv2025

Effects of Matter Lagrangian in f(Q,T) Gravity: The Accelerating Cosmological Model

We investigate the logarithmic form of $f(Q,T)$ gravity with two different choices of matter Lagrangian such as: $\mathcal{L}_m = p$ and $\mathcal{L}_m = -ρ$. The parameters of the model has been constrained using Cosmic Chronometers (CC) in combination with DES-SN5YR and Pantheon$^+$ Type Ia supernova datasets. We have observed that the deceleration parameter shows a smooth transition from deceleration to acceleration phase and the effective equation of state parameter ($ω$) approaches to $-1$ at late times. The $Om(z)$ diagnostic exhibits a decreasing profile, confirming quintessence-like behavior, and the statefinder analysis demonstrates trajectories that remain near the $Λ$CDM fixed point but deviate into the quintessence region. The evolution of the density parameters satisfies the flatness condition, and the predicted age of the Universe lies within $t_0 \sim 13.7-14.3$ Gyr, consistent with CMB and stellar estimates. The findings indicate that the logarithmic model successfully reproduces the late-time accelerated expansion for both the choices of the matter Lagrangian.

gr-qc↗

arXiv2025

The scalar-torsion gravity corrections in the first-order inflationary models

The corrections to the cosmological models induced by non-minimal coupling between scalar field and torsion are considered. To determine these corrections in explicit form, the power-law parametrization of these corrections are proposed. The estimates of possible influence of non-minimal coupling between scalar field and torsion on cosmological parameters for inflationary models implying linear relation between tensor-to-scalar ratio and spectral index of scalar perturbations are obtained. A procedure for verifying these inflationary models due to the observational constraints on the values of cosmological perturbation parameters is also considered.

gr-qc↗

arXiv2024

Reconstruction the scalar-torsion gravity version from the frame of exact cosmological solutions

We consider cosmological models based on the scalar-torsion gravity implying non-minimal coupling between torsion and the scalar field with certain relations between model's parameters. Based on observational constraints on the values of the parameters of cosmological perturbations, the type of the coupling was determined. It was noted that any inflationary models constructed on the basis of the proposed approach can be verified by observational constraints.

gr-qc↗

arXiv2024

Dynamical system analysis in modified Galileon cosmology

In this paper, we have investigated the phase space analysis in modified Galileon cosmology, where the Galileon term is considered a coupled scalar field, $F(ϕ)$. We focus on the exponential type function of $F(ϕ)$ and the three well-motivated potential functions $V(ϕ)$. We obtain the critical points of the autonomous system, along with their stability conditions and cosmological properties. The critical points of the autonomous system describe different phases of the Universe. In the results of our analysis, we have found the scaling solution for critical points, which determine different evolutionary eras for the Universe. The dark-energy-dominated critical points show stable behavior and indicate the Universe's late-time cosmic acceleration phase. Further, the results are examined with the cosmological data sets of the Hubble rate $H(z)$ and the Supernovae Ia.

gr-qc↗

arXiv2023

Modified inflationary models based on scalar-torsion gravity

In this work, we consider the corrections to the cosmological models based on the teleparralel equivalent of general relativity and the scalar-torsion gravity implying non-minimal coupling between scalar field and torsion. To determine these corrections, we consider a power-law parameterization of the deviations between teleparralel equivalent of general relativity and the scalar-torsion gravity. The impact of these deviations on cosmological dynamics, scalar field potential and parameters of cosmological perturbations is considered for different inflationary models.

gr-qc↗

arXiv2022

New method of exponential potentials reconstruction based on given scale factor in phantonical two-field models

We investigate two-field cosmological model with phantom and canonical fields (phantonical model as a generalisation of the quintom model for global universe evolution, including early inflationary stage). The model is represented as the chiral cosmological model with the target space conformal to 2D pseudo-Euclidean space. We found three sorts of exact solutions for a constant potential by direct integration of dynamic equations and proposed new method of exact solution construction also extended for e-folds N-formalism for the case of non-constant exponential potential. We show that the exact solutions of cosmological dynamic equations can be obtained in explicit form for any type of scale factor evolution $a(t)$ which implies the explicit inverse dependence $t=t(a)$, considering the quasi de Sitter expansion of the universe with non-negligible kinetic energies of scalar fields and showing that the appeared effective cosmological constant can be considered as the source of second accelerated expansion of the universe. Further we analyze cosmological perturbations in the two-field model under consideration reducing it to the single field one. Such transition give us the way of cosmological parameters calculation and comparison them to observational data. We find that in proposed two-field cosmological model the isocurvature perturbations are negligible, and observable curvature perturbations are induced by adiabatic modes only. The series of phantonical models based on exact inflationary solutions are represented, and it is shown the correspondence to observational data for these models.

gr-qc↗

arXiv2020

Exact and slow-roll solutions for exponential power-law inflation connected with f(R) gravity and observational constraints

We investigate an ability of the exponential power-law inflation to be phenomenologically correct model of the early universe. GR scalar cosmology equations we study in Ivanov-Salopek-Bond (or Hamilton-Jacobi like) representation where the Hubble parameter $H$ is the function of a scalar field $ϕ$. Such approach admits calculation of the potential for given $H(ϕ)$ and consequently reconstruction of $f(R)$ gravity in parametric form. By this manner the Starobinsky potential and non-minimal Higgs potential (and consequently the corresponding $f(R)$ gravity) were reconstructed using constraints on model's parameters. Also comparison to observation (PLANCK 2018) data shows that both models give correct values for scalar spectral index and tensor-to-scalar ratio under wide range of exponential-power-law model's parameters.

gr-qc↗

arXiv2020

Generalized scalar-tensor theory of gravity reconstruction from physical potentials of a scalar field

We describe how to reconstruct generalized scalar-tensor gravity (GSTG) theory, which admits exact solutions for physical type of the potentials. Our consideration deals with cosmological inflationary models based on GSTG with non-minimal coupling of a (non-canonical) scalar field to the Ricci scalar. The basis of proposed approach to the analysis of these models is a priori specified relation between the Hubble parameter $H$ and a function of non-minimal coupling $F=1+δF$ as $H\propto\sqrt{F}$. Deviations from Einstein gravity $δF$ induce a corresponding deviations of the potential $δV$ from a constant value and modify the dynamics from pure de Sitter exponential expansion. We analyze the models with exponential power-law evolution of the scale factor and we find the equations of influence of non-minimal coupling, choosing it in the special form, on the potential and kinetic energies. Such consideration allows us to substitute the physical potential into obtained equations and then to calculate the non-minimal coupling function and kinetic term that are define GSTG parameters. With this method, we reconstruct GSTG for polynomial, exponential, Higgs, Higgs-Starobinsky and Coleman-Weinberg potentials. Special attention we pay to parameters of cosmological perturbations and prove correspondence obtained solutions to observational data from Planck.

gr-qc↗

arXiv2020

Bound gravitational waves in a dielectric medium and a constant magnetic field

A description is made of the process of excitation of bound longitudinal-transverse gravitational waves during the propagation of electromagnetic waves in a dielectric medium. It is shown that the speed of such gravitational waves is less than the speed of light in a vacuum and coincides with the speed of an electromagnetic wave in matter. A description of the propagation of a bound gravitational waves in a dielectric in the presence of a constant magnetic field is suggested as well. It is claimed that these gravitational waves in a dielectric medium are forced ones and they cannot exist in a free state.

gr-qc↗

arXiv2020

On the gravitational waves coupled with electromagnetic waves

A description is made of the process of excitation of coupled longitudinal-transverse gravitational waves during the propagation of a strong electromagnetic wave in a vacuum and when a standing electromagnetic wave exists in the Fabry-Perot resonator. It is shown that such waves lead to the appearance of transverse gravitational waves in empty space. It was established that two standing high-frequency electromagnetic waves in a Fabry-Perot resonator with close frequencies cause the appearance of a low-frequency transverse gravitational wave in empty space.

gr-qc↗

arXiv2019

Superpotential method for chiral cosmological models connected with modified gravity

We consider the Chiral Cosmological Models (CCMs) and modified gravity theories associated with them. Generalization of the superpotential method for a general CCM with several scalar fields is performed, and the method of construction CCMs admitting exact solutions is developed. New classes of exact solutions in the two-component CCM connected with an $f(R)$ gravity model with an additional scalar field have been constructed. We construct new cosmological solutions for a diagonal metric of the target space, including modified power-law solutions. In particular, we propose the reconstruction procedure based on the superpotential method and present examples of kinetic part reconstruction for periodic and hyperbolic Hubble parameters. We also focus on a cyclic type of Universe dubbed the Quasi-Steady State (QSS) model, with the aim of constructing single- and double-field potentials for one and the same behaviour of the Hubble parameter using the developed superpotential method for the CCM. The realization of this task includes a new set of solutions for a CCM with a scale factor characterized by the QSS theory. We also propose a method for reducing the two-field CCM to the single scalar field model.

gr-qc↗