Deceleration parameter

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

An Interacting Two-Fluid Scenario for Dark Energy in an FRW Universe

Abstract: We study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic Friedmann—Robertson—Walker (FRW) model filled with barotropic fluid and dark energy. To obtain the deterministic solution we choose the scale factor , which yields a time-dependent deceleration parameter (DP). In doing so, we consider the case minimally coupled with dark energy to the perfect fluid as well as direct interaction with it.

LRS Bianchi type-I cosmological model in f ( R , T ) theory of gravity with Λ ( T )

Abstract: The locally rotationally symmetric (LRS) Bianchi type-I cosmological models have been investigated in f(R,T) theory of gravity, where R is the Ricci scalar and T is the trace of the energy momentum tensor, for some choices of the functional f(R,T)=f 1(R)+f 2(T). The exact solutions of the field equations are obtained for the linearly varying deceleration parameter q(t) proposed by Akarsu and Dereli (2012). Keeping an eye on the accelerating nature of the universe in the present epoch, the dynamics and physical behaviour of the models have been discussed. It is interesting to note that in one of the model, the universe ends with a big rip. By taking different functional forms for f 2(T) we have investigated whether or not the Big Rip can be avoided. We found that, the Big Rip situation can not be avoided and may be inherent in the linearly varying deceleration parameter. We have also applied the State-finder diagnostics to get the geometrical dynamics of the universe at different phases.

f( R) theories of gravity in the Palatini approach matched with observations

Abstract: We investigate the viability of f(R) theories in the framework of the Palatini approach as solutions to the problem of the observed accelerated expansion of the universe. Two physically motivated popular choices for f(R) are considered,: power law, f(R) = β Rn, and logarithmic, f(R) = α ln R. Under the Palatini approach, both Lagrangians give rise to cosmological models comprising only standard matter and undergoing a present phase of accelerated expansion. We use the Hubble diagram of type Ia Supernovae and the data on the gas mass fraction in relaxed galaxy clusters to see whether these models are able to reproduce what is observed and to constrain their parameters. It turns out that they are indeed able to fit the data with values of the Hubble constant and of the matter density parameter in agreement with some model independent estimates, but the today deceleration parameter is higher than what is measured in the concordance ΛCDM model.

Three thermodynamically-based parameterizations of the deceleration parameter

Abstract: We propose and constrain with the latest observational data, three model-independent parametrizations of the cosmic deceleration parameter $q(z)$. They are well behaved and stay finite at all redshifts. We construct them by fixing the value of $q$ at high redshift, $q(z\ensuremath{\gg}1)=1/2$ (as demanded by cosmic structure formation), and at the far future $q(z=\ensuremath{-}1)=\ensuremath{-}1$, and smoothly interpolating $q(z)$ between them. The fixed point at $z=\ensuremath{-}1$ is not arbitrarily chosen; it readily follows from the second law of thermodynamics. This fairly reduces the ample latitude in parametrizing $q(z)$.