Evolution of FLRW universe in Brans-Dicke gravity theory

Abstract

This study aims to examine the dynamics of flat Friedmann-Lemaitre-Robertson-Walker (FLRW) model of universe with time varying cosmological constant $\Lambda (t)$ in Brans-Dicke theory of gravity. The authors find a solution of the field equations using simple parametrization of scale factor $a(t)$ i.e. $a(t)=\exp \{(\alpha t+\beta )^{p}\}$ , and power law relation between $a(t)$ and Brans-Dicke scalar field $\phi $ . The derived cosmological model shows transition from early cosmic deceleration to present cosmic acceleration. Such feature of cosmic expansion is in agreement with recent empirical observations. The behaviour of cosmographic parameters such as Hubble parameter, deceleration parameter, jerk, snap and lerk parameters is examined graphically. It is observed that model behaves like $\Lambda CDM$ model in late cosmic evolution. We also use statefinder and Om diagnostic tools to differentiate various dark energy models from $\Lambda CDM$ model. Moreover, model parameter $p$ and present value of deceleration parameter $q_{0}$ is also estimated using Hubble data set and Pantheon Type 1a supernova data set.