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Sergey V. Chervon

Publications and source records attributed to Sergey V. Chervon.

13 recordsLinked to original sources
arXiv2024

Propagation of light and retarded time of radiation in a strong gravitational wave

For the strong gravitational wave model, an explicit transformation is obtained from a privileged coordinate system with a wave variable to a synchronous reference frame with separation of time and space variables. In a synchronous reference frame, a general form of the gravitational wave metric, solutions to the equations of trajectories for test particles in the Hamilton-Jacobi formalism, a solution to the eikonal equation for radiation, and a form of equations for the light cone of an observer in a gravitational wave were found. Using the obtained relations, the form the retarded time of radiation in the gravitational wave was found. The general relations obtained can be applied both in Einstein general theory of relativity and in modified theories of gravity. The obtained relations were applied in the work for an exact model of a gravitational wave in the Bianchi type VI universe based on an exact solution of Einstein vacuum equations.

gr-qc↗
arXiv2022

Black holes and wormholes in $f(R)$ gravity with a kinetic curvature scalar

We study the chiral self-gravitating model (CSGM) of a special type in the spherically symmetric static spacetime in Einstein frame. Such CSGM is derived, by virtue of Weyl conformal transformation, from a gravity model in the Jordan frame corresponding to a modified $f(R)$ gravity with a kinetic scalar curvature. We investigate the model using harmonic coordinates and consider a special case of the scaling transformation from the Jordan frame. We find classes of solutions corresponding to a zero potential and we investigate horizons, centers and the asymptotic behavior of the obtained solutions. Other classes of solutions (for the potential not equal to zero) are found using a special relation (ansatz) between the metric components. Investigations of horizons, centers and asymptotic behavior of obtained solutions for this new case are performed as well. Comparative analysis with the solutions obtained earlier in literature is made.

gr-qc↗
arXiv2019

Reconstruction of GR cosmological solutions in modified gravity theories

We study the special class of the exact solutions in cosmological models based on the Generalized Scalar-Tensor Gravity with non-minimal coupling of a scalar field to the Ricci scalar and to the Gauss-Bonnet scalar in 4D Friedmann universe corresponding to similar ones in GR. The parameters of cosmological perturbations in such models correspond to the case of Einstein gravity with a high precision. As the example of proposed approach, we obtain the exact solutions for the power-law and exponential power-law inflation.

gr-qc↗
arXiv2018

The method of generating functions in exact scalar field cosmology

Exact solutions construction in scalar fields cosmology is of growing interest. In this work we review the results which obtained with the help of one of the most effective method. Namely, the method of generating functions for exact solutions construction in the scalar field cosmology. We also included into debate the superpotential method which may be considered as the bridge to slow roll approximation equations. Basing on the review, we suggested classification for the generating functions and found connection for all of them with the superpotential.

gr-qc↗
arXiv2017

A new approach to exact solutions construction in scalar cosmology with a Gauss-Bonnet term

We study the cosmological model based on Einstein-Gauss-Bonnet gravity with non-minimal coupling of a scalar field to a Gauss-Bonnet term in 4D Friedmann universe. We show how constructing the exact solutions by the method based on a confrontation of the Hubble parameter in the model under consideration with that in a standard scalar field inflationary cosmology.

gr-qc↗
arXiv2017

New Exact Solutions for a Chiral Cosmological Model in 5D EGB Gravity

We consider a chiral cosmological model in the framework of Einstein-Gauss-Bonnet cosmology. Using a decomposition of the latter equations in such a way that the first chiral field is responsible for the Einstein part of the model, while the second field together with the kinetic interaction is connected with the Gauss--Bonnet part of the theory, we find new exact solutions for the 2-component chiral cosmological model with and without the kinetic interaction between fields.

gr-qc↗
arXiv2017

On calculation of the cosmological parameters in exact models of inflation

We discuss a method of calculating the key cosmological parameters on the basis of a selected scale factor by using exact solutions of the background equations. We specify the formulas for calculating the power spectrum, the spectral indices and their ratios, and the ratio of squared amplitudes of scalar and tensor perturbations. We obtain, for the first time, expressions for the basic cosmological parameters in terms of the scalar factor value at the instant of crossing the cosmological horizon. In this case, the cosmological parameters are calculated for a wide class of exact models. They are compared with their analogs derived in the slow-rolling approximation.

gr-qc↗
arXiv2017

Exact Inflation in Einstein-Gauss-Bonnet Gravity

We study cosmological inflation in the Einstein gravity model, where additionally the Gauss-Bonnet term non-minimally coupled to a scalar field is included. We prove that inflationary solutions of exponential and power-law types are allowable and we found few examples of them. We also proposed the method of the exact inflationary solutions construction for a single scalar field with given scale factor and Gauss-Bonnet coupling term in the spatially flat Friedmann-Robertson-Walker Universe on the basis of connection with standard inflation and using special anzatses. With one special anzats we presented the system of equations in the form which allowed generation of exact solutions (at least in quadratures) of wide class by setting the scale factor.

gr-qc↗
arXiv2014

$σ$CDM coupled to radiation. Dark energy and Universe acceleration

Recently the Chiral Cosmological Model (CCM) coupled to cold dark matter (CDM) has been investigated as $σ$CDM model to study the observed accelerated expansion of the Universe. Dark sector fields (as Dark Energy content) coupled to cosmic dust were considered as the source of Einstein gravity in Friedmann-Robertson-Walker (FRW) cosmology. Such model had a beginning at the matter-dominated era. The purposes of our present investigation are two folds: to extend < > of the $σ$CDM for earlier times to radiation-dominated era and to take into account variation of the exponential potential via variation of the interaction parameter $λ$. We use Markov Chain Monte Carlo (MCMC) procedure to investigate possible values of initial conditions constrained by the measured amount of the dark matter, dark energy and radiation component today. Our analysis includes dark energy contribution to critical density, the ratio of the kinetic and potential energies, deceleration parameter, effective equation of state and evolution of DE equation of state with variation of coupling constant $λ$. A comparison with the $Λ$CDM model was performed. A new feature of the model is the existence of some values of potential coupling constant, leading to a $σ$CDM solution without transit into accelerated expansion epoch.

gr-qc↗
arXiv2014

An Emergent Universe supported by chiral cosmological fields in Einstein--Gauss--Bonnet gravity

We propose the application of the chiral cosmological model (CCM) for the Einstein--Gauss--Bonnet (EGB) theory of gravitation with the aim of finding new models of the Emergent Universe (EmU) scenario. We analysed the EmU supported by two chiral cosmological fields for a spatially flat universe, while we have used three chiral fields when we investigated open and closed universes. To prove the validity of the EmU scenario we fixed the scale factor and found the exact solution by decomposition of EGB equations and solving the chiral field dynamics equation. To this end, we suggested the decomposition of the EGB equations in such a way that the first chiral field is responsible for the Einstein part of the model, while the second field, together with kinetic interaction term, is connected with the Gauss--Bonnet part of the theory. We proved that both fields are phantom ones under this decomposition, and that the model has a solution if the kinetic interaction between the fields equals a constant. We have presented the exact solution in terms of cosmic time. This was done for a spatially flat universe. In the case of open and closed universes we introduced the third chiral field (canonical for closed and phantom for open universe) which is responsible for the EGB and curvature parts. The solution of the third field equation is obtained in quadratures. Thus we have proved that the CCM is able to support EmU scenario in EGB gravity for spatially flat, open and closed universes.

gr-qc↗
arXiv2014

Unified dark matter and dark energy description in a chiral cosmological model

We show the way of dark matter and dark energy presentation via ansatzs on the kinetic energies of the fields in the two-component chiral cosmological model. To connect a kinetic interaction of dark matter and dark energy with observational data the reconstruction procedure for the chiral metric component $h_{22}$ and the potential of (self)interaction $V$ has been developed. The reconstruction of $h_{22}$ and $V$ for the early and later inflation have been performed. The proposed model is confronted to $ΛCDM$ model as well.

gr-qc↗
arXiv2013

New exact cosmologies on the brane

We develop a method for constructing exact cosmological solutions in brane world cosmology. New classes of cosmological solutions on Randall-Sandrum brane are obtained. The superpotential and Hubble parameter are represented in quadratures. These solutions have inflationary phases under general assumptions and also describe an exit from the inflationary phase without a fine tuning of the parameters. Another class solutions can describe the current phase of accelerated expansion with or without possible exit from it.

astro-ph.CO↗