Cosmic acceleration in a model of scalar-tensor gravitation

Abstract

In this paper we consider a model of scalar-tensor theory of gravitation in which the scalar field, $ϕ$ determines the gravitational coupling G and has a Lagrangian of the form, $\mathcal{L}_ϕ =-V(ϕ)\sqrt{1 - \partial_μϕ\partial^μϕ}$. We study the cosmological consequence of this theory in the matter dominated era and show that this leads to a transition from an initial decelerated expansion to an accelerated expansion phase at the present epoch. Using observational constraints, we see that the effective equation of state today for the scalar field turns out to be $p_ϕ=w_ϕρ_ϕ$, with $w_ϕ=-0.88$ and that the transition to an accelerated phase happened at a redshift of about 0.3.