arXiv subjects

A. N. Makarenko

Publications and source records attributed to A. N. Makarenko.

11 recordsLinked to original sources

arXiv2019

Viscous Accelerating Universe with Non-linear and Logarithmic Equation of State Fluid

We describe the accelerated expansion of the late-time universe using a generalized equation of state (EoS) when account is taken of bulk viscosity. We assume a homogeneous and isotropic Friedmann-Robertson-Walker spacetime. Solutions of the gravitational equations for dark energy are obtained in implicit form. Characteristic properties of the Universe evolution in the presence of the viscosity effects are discussed. Finally, the dynamics of the accelerated expansion of the viscous universe is discussed, on the basis of a modified logarithmic-corrected EoS.

gr-qc↗

arXiv2016

On a phenomenology of the accelerated expansion with a varying ghost dark energy

Subject of our study it is the accelerated expansion of the large scale universe, where a varying ghost dark energy can take the role of the dark energy. The model of the varying ghost dark energy considered in this work it is a phenomenological modification of the ghost dark energy. Recently, three other phenomenological models of the varying ghost dark energy have been suggested and the model considered in this work will complete the logical chain of considered modifications. The best fit of theoretical results to the luminosity distance, has been used to obtain preliminary constraints on the parameters of the models. This does help us to reduce amount of discussion. On the other hand, detailed comparison of theoretical results with observational data has been left as a subject of another discussion elsewhere. Moreover, a look to considered models via $Om$ and statefinder hierarchy analysis is presented and discussed for different forms of interaction between the varying ghost dark energy and cold dark matter.

gr-qc↗

arXiv2015

Bounce Loop Quantum Cosmology Corrected Gauss-Bonnet Gravity

We develop a Gauss-Bonnet extension of Loop Quantum Cosmology, by introducing holonomy corrections in modified $F(\mathcal{G})$ theories of gravity. Within the context of our formalism, we provide a perturbative expansion in the critical density, a parameter characteristic of Loop Quantum Gravity theories, and we result in having leading order corrections to the classical $F(\mathcal{G})$ theories of gravity. After extensively discussing the formalism, we present a reconstruction method that makes possible to find the Loop Quantum Cosmology corrected $F(\mathcal{G})$ theory that can realize various cosmological scenarios. Specifically, we studied exponential and power-law bouncing cosmologies, emphasizing on the behavior near the bouncing point and in some cases, the behavior for all the values of the cosmic time is obtained. We exemplify our theoretical constructions by using bouncing cosmologies, and we investigate which Loop Quantum Cosmology corrected Gauss-Bonnet modified gravities can successfully realize such cosmologies.

gr-qc↗

arXiv2014

Cosmological models with the spinor and non-minimally interacting scalar field

The solution to the current extending Universe problem, and the description of all stages of evolution compels scientists to consider various cosmological models. Scalar - tensor models are rather simple and also allow us to clearly define the separate stages of evolution. Furthermore, other cosmological models are reduced. Our work takes into consideration the non-minimally interacted scalar field and the spinor field. The spinor field has been considered to establish a better understanding of the stages of evolution in our Universe.

gr-qc↗

arXiv2013

Accelerating and decelerating cosmology from spinor and scalar fields non-minimally coupled with f(R) gravity

In this paper we investigate the accelerating and decelerating cosmological models with non-linear spinor fields and non-minimal interaction of $f(R)$ gravity with a scalar field. We combine two different approaches to the description of dark energy: modified gravity theory and introduction of the additional fields. Solutions for the FRW universe with power-law scale factor are reconstructed for the model under consideration with specific choice for scalar and spinor potentials. It is explained the role of scalar and spinor potentials as well as f(R) function for emergence of accelerating or decelerating cosmology.

gr-qc↗

arXiv2012

Multiple $Λ$CDM cosmology with string landscape features and future singularities

Multiple $Λ$CDM cosmology is studied in a way that is formally a classical analog of the Casimir effect. Such cosmology corresponds to a time-dependent dark fluid model or, alternatively, to its scalar field presentation, and it motivated by the string landscape picture. The future evolution of the several dark energy models constructed within the scheme is carefully investigated. It turns out to be almost always possible to choose the parameters in the models so that they match the most recent and accurate astronomical values. To this end, several universes are presented which mimick (multiple) $Λ$CDM cosmology but exhibit Little Rip, asymptotically de Sitter, or Type I, II, III, and IV finite-time singularity behavior in the far future, with disintegration of all bound objects in the cases of Big Rip, Little Rip and Pseudo-Rip cosmologies.

gr-qc↗

arXiv2012

From Big to Little Rip in modified F(R,G) gravity

We discuss the cosmological reconstruction in modified Gauss-Bonnet (GB) gravity. It is demonstrated that the modified GB gravity may describe the most interesting features of late-time cosmology. We derive explicit form of effective phantom cosmological models ending by the finite-time future singularity (Big Rip) and without singularities in the future (Little Rip).

gr-qc↗

arXiv2009

The nature of singularity in multidimensional anisotropic Gauss-Bonnet cosmology with a perfect fluid

We investigate dynamics of (4+1) and (5+1) dimensional flat anisotropic Universe filled by a perfect fluid in the Gauss-Bonnet gravity. An analytical solutions valid for particular values of the equation of state parameter $w=1/3$ have been found. For other values of $w$ structure of cosmological singularity have been studied numerically. We found that for $w > 1/3$ the singularity is isotropic. Several important differences between (4+1) and (5+1) dimensional cases are discussed.

gr-qc↗

arXiv2006

Stationary vs. singular points in an accelerating FRW cosmology derived from six-dimensional Einstein-Gauss-Bonnet gravity

Six-dimensional Einstein-Gauss-Bonnet gravity (with a linear Gauss-Bonnet term) is investigated. This theory is inspired by basic features of results coming from string and M-theory. Dynamical compactification is carried out and it is seen that a four-dimensional accelerating FRW universe is recovered, when the two-dimensional internal space radius shrinks. A non-perturbative structure of the corresponding theory is identified which has either three or one stable fixed points, depending on the Gauss-Bonnet coupling being positive or negative. A much richer structure than in the case of the perturbative regime of the dynamical compactification recently studied by Andrew, Bolen, and Middleton is exhibited.

hep-th↗

arXiv2004

Wormholes in the Braneworld

We discuss brane wormhole solution when classical brane action contains 4d curvature. The equations of motion for the cases with R=0 and $R\ne 0$ are obtained. Their numerical solutions corresponding to wormhole are found for specific boundary conditions.

gr-qc↗

arXiv2003

Kantowski-Sachs Brane Cosmology

We consider brane Kantowski-Sachs Universe when bulk space is five-dimensional Anti-deSitter space. The corresponding cosmological equations with perfect fluid are written. For several specific choices of relation between energy and pressure it is found the behavior of scale factors at early time. In particulary, for $γ=3/2$ Kantowski-Sachs brane cosmology is modified to become the isotropic one, while for $γ=1$ it remains the anisotropic cosmology in the process of evolution.

gr-qc↗