Deceleration parameter

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

Tsallis holographic model of dark energy: Cosmic behaviour, statefinder analysis and $\omega_D-\omega_D'$ pair in the non-flat universe

Abstract: The paper investigates the Tsallis holographic dark energy (THDE) model in accordance with the apparent horizon as an infrared cut-off, in a non-flat universe. The cosmological evolution of the deceleration parameter and equation of state of THDE model are calculated. The evolutionary trajectories are plotted for the THDE model for distinct values of the Tsallis parameter $\delta$ besides distinct spatial curvature contributions, in the statefinder $(r, s)$ parameter-pairs and $\omega_{D}-\omega^{'}_{D}$ plane, considering the present value of dark energy density parameter $\Omega_{D0} $, $\Omega_{D0}=0.72$, in the light of $WMAP + eCMB + BAO + H_{0}$ observational data. The statefinder and $\omega_{D}-\omega^{'}_{D}$ plane plots specify the feature of the THDE and demonstrate the separation between this framework and other models of dark energy.

New holographic dark energy model with constant bulk viscosity in modified $$ gravity theory

Abstract: The aim of this paper is to study new holographic dark energy (HDE) model in modified $f(R,T)$ gravity theory within the framework of a flat Friedmann-Robertson-Walker model with bulk viscous matter content. It is thought that the negative pressure caused by the bulk viscosity can play the role of dark energy component, and drive the accelerating expansion of the universe. This is the motive of this paper to observe such phenomena with bulk viscosity. In the specific model $f(R,T)=R+\lambda T$ , where $R$ is the Ricci scalar, $T$ the trace of the energy-momentum tensor and $\lambda $ is a constant, we find the solution for non-viscous and viscous new HDE models. We analyze new HDE model with constant bulk viscosity, $\zeta =\zeta _{0}= \text{const.}$ to explain the present accelerated expansion of the universe. We classify all possible scenarios (deceleration, acceleration and their transition) with possible positive and negative ranges of $\lambda $ over the constraint on $\zeta _{0}$ to analyze the evolution of the universe. We obtain the solutions of scale factor and deceleration parameter, and discuss the evolution of the universe. We observe the future finite-time singularities of type I and III at a finite time under certain constraints on $\lambda $ . We also investigate the statefinder and $\mathit{Om}$ diagnostics of the viscous new HDE model to discriminate with other existing dark energy models. In late time the viscous new HDE model approaches to $\varLambda \mathit{CDM}$ model. We also discuss the thermodynamics and entropy of the model and find that it satisfies the second law of thermodynamics.

Probing bulk viscous matter-dominated models with gamma-ray bursts

Abstract: � in the range 0 < ˜ < 3, being so consistent with previous probes; we also determined the deceleration parameter q0 and the redshift of transition to accelerated expansion. Besides we present an updated analysis of the model with CMB5-year data and CMB7-year data, as well as with the baryon acoustic peak BAO. From the statistics with CMB it turns out that the model does not describe in a feasible way the far far epoch of recombination of the universe, but is in very good concordance for epochs as far as z � 8.1 till present.

Probing the cosmic acceleration history and the properties of dark energy from the ESSENCE supernova data with a model independent method

Abstract: With a model independent method the expansion history H(z), the deceleration parameter q(z) of the universe and the equation of state w(z) for the dark energy are reconstructed directly from the 192 Sne Ia (type Ia supernovae) data points which are contained in the new ESSENCE (Equation of State: Supernovae Trace Cosmic Expansion) Sne Ia data and the high redshift Sne Ia data. We find that the evolving properties of q(z) and w(z) reconstructed from the 192 Sne Ia data seem to be weaker than those obtained from the Gold set, but stronger than those from the SNLS (Supernova Legacy Survey) set. With a combination of the 192 Sne Ia and BAO (Baryonic Acoustic Oscillation) data, a tight constraint on Ωm0 is obtained. At the 1σ confidence level Ωm0 = 0.278−0.023+0.024, which is highly consistent with the values from the Gold + BAO and SNLS + BAO data.