Deceleration parameter

About: Deceleration parameter is a research topic. Over the lifetime, 1776 publications have been published within this topic receiving 89440 citations.

LRS Bianchi type -V cosmology with heat flow in scalar: tensor theory

Abstract: In this paper we present a spatially homogeneous locally rotationally symmetric (LRS) Bianchi type -V perfect fluid model with heat conduction in scalar tensor theory proposed by Saez and Ballester. The field equations are solved with and without heat conduction by using a law of variation for the mean Hubble parameter, which is related to the average scale factor of metric and yields a constant value for the deceleration parameter. The law of variation for the mean Hubble parameter generates two types of cosmologies one is of power -law form and second the exponential form. Using these two forms singular and non -singular solutions are obtained with and without heat conduction. We observe that a constant value of the deceleration parameter is reasonable a description of the different phases of the universe. We arrive to the conclusion that the universe decelerates for positive value of deceleration parameter where as it accelerates for negative one. The physical constraints on the solutions of the field equations, and, in particular, the thermodynamical laws and energy conditions that govern such solutions are discussed in some detail.The behavior of the observationally important parameters like expansion scalar, anisotropy parameter and shear scalar is considered in detail.

A Plane-Symmetric Magnetized Inhomogeneous Cosmological Models of Perfect Fluid Distribution with Variable Magnetic Permeability in Lyra Geometry

Abstract: A plane-symmetric magnetized inhomogeneous cosmological model of the universe with time dependent gauge function β for perfect fluid distribution with variable magnetic permeability within the framework of Lyra geometry is investigated. The source of the magnetic field is due to an electric current produced along the z-axis. Thus F12 is the only non-vanishing component of electromagnetic field tensor Fij. To get a deterministic solution of Einstein’s modified field equations, the free gravitational field is assumed to be Petrov type-II non-degenerate. For our derived model we obtain the deceleration parameter q=−1 as in the case of de Sitter universe. It has been found that the displacement vector β(t) behaves like cosmological term Λ in the normal gauge treatment and the solution is consistent with the observations. The displacement vector β(t) affects entropy. Some physical and geometric properties of the model are also discussed.

Statefinder diagnosis for holographic dark energy models in modified \(f(R,T)\) gravity

Abstract: In this paper we consider the non-viscous and viscous holographic dark energy models in modified $f(R,T)$ gravity in which the infra-red cutoff is set by the Hubble horizon. We find power-law and exponential form of scale factor for non-viscous and viscous models, respectively. It is shown that the Hubble horizon as an infra-red cut-off is suitable for both the models to explain the recent accelerated expansion. In non-viscous model, we find that there is no phase transition. However, viscous model explains the phase transition from decelerated phase to accelerated phase. The cosmological parameters like deceleration parameter and statefinder parameters are discussed to analyze the dynamics of evolution of the Universe for both the models. The trajectories for viscous model are plotted in $r$ - $s$ and $r$ - $q$ planes to discriminate our model with the existing dark energy models which show the quintessence like behavior.

Cosmological and thermodynamics analysis in Weyl gravity

Abstract: In the framework of modified Weyl gravity, we observe the equilibrium picture of the thermodynamical laws for flat Friedmann–Robertson–Walker metric with chameleon scalar field and analyze the validity of the generalized second law of thermodynamics and thermal equilibrium condition for Hubble horizon along with Bekenstien–Hawking entropy. Also, we examine the effective equation of state parameter as well as the square speed of sound. By assuming four different choices of deceleration parameter, we investigate the behavior of equation of state parameter as well as the square speed of sound. The validity of generalized second law of thermodynamics and thermal equilibrium condition is also checked by taking the observational values of the model parameters from CC+$$H_o$$ dataset.

Cosmology In Terms Of The Deceleration Parameter. Part II

Abstract: In the early seventies, Alan Sandage defined cosmology as the search for two numbers: Hubble parameter ${{H}_{0}}$ and deceleration parameter ${{q}_{0}}$. The first of the two basic cosmological parameters (the Hubble parameter) describes the linear part of the time dependence of the scale factor. Treating the Universe as a dynamical system it is natural to assume that it is non-linear: indeed, linearity is nothing more than approximation, while non-linearity represents the generic case. It is evident that future models of the Universe must take into account different aspects of its evolution. As soon as the scale factor is the only dynamical variable, the quantities which determine its time dependence must be essentially present in all aspects of the Universe' evolution. Basic characteristics of the cosmological evolution, both static and dynamical, can be expressed in terms of the parameters ${{H}_{0}}$ and ${{q}_{0}}$. The very parameters (and higher time derivatives of the scale factor) enable us to construct model-independent kinematics of the cosmological expansion. Time dependence of the scale factor reflects main events in history of the Universe. Moreover it is the deceleration parameter who dictates the expansion rate of the Hubble sphere and determines the dynamics of the observable galaxy number variation: depending on the sign of the deceleration parameter this number either grows (in the case of decelerated expansion), or we are going to stay absolutely alone in the cosmos (if the expansion is accelerated). The intended purpose of the report is reflected in its title --- "Cosmology in terms of the deceleration parameter". We would like to show that practically any aspect of the cosmological evolution is tightly bound to the deceleration parameter. It is the second part of the report. The first part see here http://arxiv.org/abs/1502.00811