Deceleration parameter

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

Cosmological constraints on polytropic gas model

Abstract: We study the polytropic gas scenario as the unification of dark matter and dark energy. We fit the model parameters by using the latest observational data including type Ia supernovae, baryon acoustic oscillation, cosmic microwave background, and Hubble parameter data. At 68.3% and 95.4% confidence levels, we find the best fit values of the model parameters as $\tilde{K}=0.742_{-0.024}^{+0.024}(1\sigma)_{-0.049}^{+0.048}(2\sigma)$ and $n=-1.05_{-0.08}^{+0.08}(1\sigma)_{-0.16}^{+0.15}(2\sigma)$. Using the best fit values of the model, we obtain the evolutionary behaviors of the equation of state parameters of the polytropic gas model and dark energy, the deceleration parameter of the universe as well as the dimensionless density parameters of dark matter and dark energy. We conclude that in this model, the universe starts from the matter dominated epoch and approaches a de Sitter phase at late times, as expected. Also the universe begins to accelerate at redshift $z_{\rm t}=0.74$. Furthermore in contrary to the $\Lambda$CDM model, the cosmic coincidence problem is solved naturally in the polytropic gas scenario.

Bianchi type-V modified holographic Ricci dark energy models in Saez-Ballester theory of gravitation

Abstract: We have investigated Bianchi type-V universe filled with matter and modified holographic Ricci dark energy in a scalar–tensor theory proposed by Saez–Ballester (Phys. Lett. A, 113, 467 (1986)). To get a determinate solution, we have used (i) hybrid expansion law (Akarsu et al. JCAP, 01, 022 (2014)), (ii) varying deceleration parameter (Mishra et al. Int. J. Theor. Phys. 52, 2546 (2013)), and (iii) linearly varying deceleration parameter (Akarsu and Dereli. Int. J. Theor. Phys. 51, 612 (2012)). The various physical and geometrical aspects of the models are also discussed.

Anisotropic Dark Energy Bianchi Type III Cosmological Models in Brans Dicke Theory of Gravity

Abstract: The main purpose of this paper is to explore the solutions of Bianchi type $III$ cosmological model in Brans Dicke theory of gravity in the background of anisotropic dark energy. We use the assumption of constant deceleration parameter and power law relation between scalar field $\phi$ and scale factor $a$ to find the solutions. The physical behavior of the solutions has been discussed using some physical quantities.

Power-Law Entropy-Corrected Holographic Dark Energy in Ho\v{r}ava-Lifshitz Cosmology with Granda-Oliveros Cut-off

Abstract: 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, $\alpha$ and $\beta$. 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 $\Omega_D'$, the Equation of State (EoS) parameter of DE $\omega_D$ and the deceleration parameter $q$. Using the parametrization of the EoS parameter $\omega_D\left(z\right)=\omega_0+\omega_1 z$, we obtain the expressions of the two parameters $\omega_0$ and $\omega_1$. 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 $\lambda$ and for different set of values of $\alpha$ and $\beta$.

Evolution of the universe in inverse and ln f ( R ) gravity

Abstract: Evolution of the universe is discussed in the framework of f(R) theory of gravity. The deceleration parameter is used to interpret various phases of the universe. We investigate the future evolution of the flat FRW universe by using observationally viable f(R) models. A numerical technique is applied to solve the evolution equation in terms of Hubble parameter which is used to explore late time acceleration of the universe. Some novel and interesting results based on the choice of coupling parameters in gravitational action are obtained. We can conclude that the considered f(R) models imply unification of matter dominated epoch with present accelerating phase of the universe.