arXiv subjects

Ratbay Myrzakulov

Publications and source records attributed to Ratbay Myrzakulov.

At least 73 records · Page 4Linked to original sources

arXiv2016

Darboux transformations and exact soliton solutions of integrable coupled spin systems related with the Manakov system

We construct a Darboux transformation of a general $su(3)$-valued spin system called the $Γ$-spin system. Using this Darboux transformation we derive a recursive formula for the soliton solutions of this spin system. Then using these results we present explicit expressions for the 1-soliton solution of the coupled $su(2)$-valued spin systems, namely, of the coupled M-LIII equation.

nlin.SI↗

arXiv2016

K-essence in Horndeski models

In this paper, we investigate a simple class of Horndeski models where the scalar field plays the role of a k-essence fluid. We present several solutions for early-time universe, namely inflation and cosmological bounce, by making use of some reconstruction technique. Moreover, we furnish the formalism to calculate perturbations in FRW space-time and we compute the spectral index and the tensor-to-scalar ratio during inflation.

gr-qc↗

arXiv2016

$k$-essence non-minimally coupled with Gauss-Bonnet invariant for inflation

In this paper, we investigated inflationary solutions for a subclass of Horndeski models where a scalar field is non-minimally coupled with the Gauss-Bonnet invariant. Examples of canonical scalar field and $k$-essence to support the early-time acceleration are considered. The formalism to calculate the perturbations in FRW universe and to derive the spectral index and the tensor-to-scalar ratio is furnished.

gr-qc↗

arXiv2016

Holographic Complexity in Gauge/String Superconductors

Following a methodology similar to \cite{Alishahiha:2015rta}, we derive a holographic complexity for two dimensional holographic superconductors (gauge/string superconductors) with backreactions. Applying a perturbation method proposed by Kanno in Ref. \cite{kanno}, we study behaviors of the complexity for a dual quantum system near critical points. We show that when a system moves from the normal phase ($T>T_c$) to the superconductor phase ($T<T_c$), the holographic complexity will be divergent.

hep-th↗

arXiv2016

Cylindrical solutions in Mimetic gravity

This paper is devoted to investigate cylindrical solutions in mimetic gravity. The explicit forms of the metric of this theory, namely mimetic-Kasner (say) have been obtained. In this study we have noticed that the Kasner's family of exact solutions needs to be reconsidered under this type of modified gravity. A no-go theorem is proposed for the exact solutions in the presence of a cosmological constant.

gr-qc↗

arXiv2016

Noether symmetry in Horndeski Lagrangian

The Noether symmetry issue for Horndeski Lagrangian has been studied. We have been proven a series of theorems about the form of Noether conserved charge (current) for irregular (not quadratic) dynamical systems. Special attentions have been made on Horndeski Lagrangian. We have been proven that for Horndeski Lagrangian always is possible to find a way to make symmetrization.

gr-qc↗

arXiv2016

Cylindrical symmetry locally isometric $AdS_{4}$ spacetime

We present a maximally symmetric vacuum spacetime, which is locally isometric anti- de Sitter, admitting closed timelike curves appear after a definite instant of time i.e., a time-machine spacetime. The spacetime is regular, free-from curvature singularities and an $4D$ extension of the Misner space in curved spacetime with identical causality violating properties.

gr-qc↗

arXiv2016

Non-local $F(R)$-mimetic gravity

In this paper, we study non-local $F(R)$-mimetic gravity. We implement mimetic gravity in the framework of non-local $F(R)$-theories of gravity. Given some specific class of models and using a potential on the mimetic field, we investigate some scenarios related to the early-time universe, namely the inflation and the cosmological bounce, compatibly with Einstein's gravity with cold dark matter at the late-time.

gr-qc↗

arXiv2016

Inflationary universe from higher derivative quantum gravity coupled with scalar electrodynamics

We study inflation for a quantum scalar electrodynamics model in curved space-time and for higher-derivative quantum gravity (QG) coupled with scalar electrodynamics. The corresponding renormalization-group (RG) improved potential is evaluated for both theories in Jordan frame where non-minimal scalar-gravitational coupling sector is explicitly kept. The role of one-loop quantum corrections is investigated by showing how these corrections enter in the expressions for the slow-roll parameters, the spectral index and the tensor-to-scalar ratio and how they influence the bound of the Hubble parameter at the beginning of the primordial acceleration. We demonstrate that the viable inflation maybe successfully realized, so that it turns out to be consistent with last Planck and BICEP2/Keck Array data.

hep-th↗

arXiv2016

Static spherically symmetric solutions in mimetic gravity: rotation curves & wormholes

In this work, we analyse static spherically symmetric solutions in the framework of mimetic gravity, an extension of general relativity where the conformal degree of freedom of gravity is isolated in a covariant fashion. Here we extend previous works by considering in addition a potential for the mimetic field. An appropriate choice of such potential allows for the reconstruction of a number of interesting cosmological and astrophysical scenarios. We explicitly show how to reconstruct such a potential for a general static spherically symmetric space-time. A number of applications and scenarios are then explored, among which traversable wormholes. Finally, we analytically reconstruct potentials which leads to solutions to the equations of motion featuring polynomial corrections to the Schwarzschild spacetime. Accurate choices for such corrections could provide an explanation for the inferred flat rotation curves of spiral galaxies within the mimetic gravity framework, without the need for particle dark matter.

gr-qc↗

arXiv2016

$k$-essence for warm inflation on the brane

In this paper, $k$-inflation is analyzed in warm braneworld scenario. A general class of $k$-essence models with power-law kinetic term is investigated and weak and strong dissipation regimes are studied. Scalar perturbations and spectral index are derived. The results are discussed and applied to specific examples.

gr-qc↗

arXiv2016

Power-Law Entropy-Corrected Holographic Dark Energy in Hořava-Lifshitz Cosmology with Granda-Oliveros Cut-off

In this paper, we study the Power Law Entropy Corrected Holographic Dark Energy (PLECHDE) model in the framework of a non-flat Universe and of Hořava-Lifshitz cosmology with infrared cut-off given by recently proposed Granda-Oliveros cut-off, which contains one term proportional to the Hubble parameter squared $H^2$ and one term proportional to the first time derivative of the Hubble parameter $\dot{H}$. Moreover, this cut-off is characterized by two constant parameters, $α$ and $β$. For the two cases corresponding to non-interacting and interacting DE and Dark Matter (DM), we derive the evolutionary form of the energy density of DE $Ω_D'$, the Equation of State (EoS) parameter of DE $ω_D$ and the deceleration parameter $q$. Using the parametrization of the EoS parameter $ω_D\left(z\right)=ω_0+ω_1 z$, we obtain the expressions of the two parameters $ω_0$ and $ω_1$. We also study the statefinder parameters $\left\{ r,s \right\}$, the snap and lerk cosmographic parameters and the squared speed of the sound $v_s^2$. We also calculate the values of the quantities we study for different values of the running parameter $λ$ and for different set of values of $α$ and $β$.

gr-qc↗

arXiv2016

Dynamical Instability of Cylindrically Symmetric Collapsing Star in Generalized Teleparallel Gravity

This paper is devoted to analyze the dynamical instability of a self-gravitating object undergoes to collapse process. We take the framework of generalized teleparallel gravity with cylindrically symmetric gravitating object. The matter distribution is represented by locally anisotropic energy-momentum tensor. We develop basic equations such as dynamical equations along with matching conditions and Harrison-Wheeler equation of state. By applying linear perturbation strategy, we construct collapse equation which is used to accomplish the instability ranges in Newtonian and post-Newtonian regimes. We find these ranges for isotropic pressure as well as reduce the results in general relativity. The unstable behavior depends on matter, metric, mass and torsion based terms.

gr-qc↗

arXiv2016

Shear-free Anisotropic Cosmological Models in f(R) Gravity

We study a class of shear-free, homogeneous but anisotropic cosmological models with imperfect matter sources in the context of f(R) gravity. We show that the anisotropic stresses are related to the electric part of the Weyl tensor in such a way that they balance each other. We also show that within the class of orthogonal f(R) models, small perturbations of shear are damped, and that the electric part of the Weyl tensor and the anisotropic stress tensor decay with the expansion as well as the heat flux of the curvature fluid. Specializing in locally rotationally symmetric spacetimes in orthonormal frames, we examine the late-time behaviour of the de Sitter universe in $f(R)$ gravity. For the Starobinsky model of f(R), we study the evolutionary behavior of the Universe by numerically integrating the Friedmann equation, where the initial conditions for the expansion, acceleration and jerk parameters are taken from observational data.

gr-qc↗

arXiv2016

Holographic Entanglement Entropy for noncommutative Anti-de Sitter space

A metric is proposed to explore the noncommutative form of the Anti-de Sitter space due to quantum effects. It has been proved that the non commutativity in AdS space induces a single component gravitoelectric field. The holographic Ryu-Takayanagi (RT) algorithm is then applied to compute the entanglement entropy in dual $CFT_2$. This calculation can be exploited to compute UV-IR cutoff dependent central charge of the certain noncommutative $CFT_2$. This non commutative computation of the entanglement entropy can be interpreted in the form of the surface/state correspondence. We have shown that non commutativity increases the dimension of the effective Hilbert space of the dual CFT.

hep-th↗

arXiv2016

On the Hojman conservation quantities in FRW Cosmology

In the present work we investigate the Hojman symmetry in FRW cosmology. In particular, we use the Hojman symmetry to find conserved quantities of particular cosmological models. Next, we study the Hojman symmetry in the scalar-tensor cosmology and find corresponding exact forms of integrals of motion. Finally, the formalism of the Hojman symmetry is extended to dynamical systems with the higher-order equations of motion.

gr-qc↗

arXiv2016

Power-law and Logarithmic Entropy Corrected Holographic Dark Energy Models in Brans-Dicke Cosmology with Granda-Oliveros Cut-Off

In this paper, the cosmological implications of the Power Law Entropy Corrected Holographic Dark Energy (PLECHDE) and the Logarithmic Entropy Corrected Holographic Dark Energy (LECHDE) models in the context of Brans-Dicke (BD) cosmology for both non-interacting and interacting DE and Dark Matter (DM) are studied. As the system infrared cut-off, we choose the recently proposed Granda-Oliveros cut-off, which contains a term proportional to the first time derivative of the Hubble parameter and one term proportional to $H^2$, i.e. the Hubble parameter squared. We obtain the expressions of three quantities, i.e. the Equation of State (EoS) parameter $ω_D$, the deceleration parameter $q$ and the evolutionary form of the energy density parameter $Ω'_D$ of the PLECHDE and LECHDE models in a non-flat Universe for non-interacting and interacting DE and DM as well. Moreover, we investigate the limiting cases corresponding to: a) absence of entropy corrections; b) Einstein's gravity; and c) concomitantly absence of entropy corrections and Einstein's gravity. Furthermore, we consider the limiting case corresponding to the Ricci scale, which is recovered for some particular values of the parameters characterizing the Granda-Oliveros scale. We also study the statefinder diagnostic and the cosmographic parameters for both models considered in this work.

physics.gen-ph↗

arXiv2016

Phase transition via entanglement entropy in $AdS_3/CFT_2$ superconductors

The purpose of this report is to provide a framework for defining phase transition processes in two dimensional holographic superconductors, and to illustrate how they are useful to be described by holographic entanglement entropy. We study holographic entanglement entropy in a two dimensional fully backrected model for holographic superconductors. We prove that phase transition could be observe using a discontinuty in the first order of entropy.

hep-th↗