Cosmic acceleration in a model of scalar-tensor gravitation

TL;DR

This paper explores a scalar-tensor gravity model with a specific scalar field Lagrangian, demonstrating it can explain the universe's transition from decelerated to accelerated expansion, consistent with observations.

Contribution

It introduces a scalar-tensor model with a Born-Infeld type scalar field Lagrangian that accounts for cosmic acceleration in the matter-dominated era.

Findings

The model predicts a transition to acceleration at redshift ~0.3.

The current effective equation of state parameter is approximately -0.88.

The theory aligns with observational constraints on cosmic acceleration.

Abstract

In this paper we consider a model of scalar-tensor theory of gravitation in which the scalar field, $\phi$ determines the gravitational coupling G and has a Lagrangian of the form, $\mathcal{L}_{\phi} =-V(\phi)\sqrt{1 - \partial_{\mu}\phi\partial^{\mu}\phi}$. 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 $p_{\phi}=w_{\phi}{\rho}_{\phi}$, with $w_{\phi}=-0.88$ and that the transition to an accelerated phase happened at a redshift of about 0.3.