Deceleration parameter

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

Statefinder and Om Diagnostics for Interacting New Holographic Dark Energy Model and Generalized Second Law of Thermodynamics

Abstract: In this work, we have considered that the flat FRW universe is filled with the mixture of dark matter and the new holographic dark energy If there is an interaction, we have investigated the natures of deceleration parameter, statefinder and $Om$ diagnostics We have examined the validity of the first and generalized second laws of thermodynamics under these interactions on the event as well as apparent horizon It has been observed that the first law is violated on the event horizon However, the generalized second law is valid throughout the evolution of the universe enveloped by the apparent horizon When the event horizon is considered as the enveloping horizon, the generalized second law is found to break down excepting at late stage of the universe

A study on the dependence of the dimensionless Brans-Dicke parameter on the scalar field and their time dependence

Abstract: The present paper reports a study on the dimensionless parameter \( \omega\) in Brans-Dicke theory. Based on a particular choice of scale factor a , we have investigated the signature flip of the deceleration parameter q to see whether the transition from decelerated to accelerated expansion of the universe is achievable under this choice of scale factor. Restrictions on the parameters obtained for this choice of scale factor have been subsequently used for discussing the Brans-Dicke parameter for two choices of scalar fields \( \phi\) . Moreover, analytical solutions for the Brans-Dicke parameter without any assumption about the scalar field have been obtained from the modified field equations through the choice of scale factor under consideration. Viable models have been obtained by comparing the results with observations.

Observational constraints to a phenomenological $f\left( R,\nabla R\right) $-model

Abstract: This paper analyses the cosmological consequences of a modified theory of gravity whose action integral is built from a linear combination of the Ricci scalar $R$ and a quadratic term in the covariant derivative of $R$. The resulting Friedmann equations are of the fifth-order in the Hubble function. These equations are solved numerically for a flat space section geometry and pressureless matter. The cosmological parameters of the higher-order model are fit using SN Ia data and X-ray gas mass fraction in galaxy clusters. The best-fit present-day $t_{0}$ values for the deceleration parameter, jerk and snap are given. The coupling constant $\beta$\ of the model is not univocally determined by the data fit, but partially constrained by it. Density parameter $\Omega_{m0}$ is also determined and shows weak correlation with the other parameters. The model allows for two possible future scenarios: there may be either a premature Big Rip or a Rebouncing event depending on the set of values in the space of parameters. The analysis towards the past performed with the best-fit parameters shows that the model is not able to accommodate a matter-dominated stage required to the formation of structure.

Anisotropic dark energy Bianchi type III cosmological models in the 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 ϕ and scale factor a to find the solutions. The physical behavior of the solutions has been discussed using some physical quantities.