Coupled quintessence and curvature-assisted acceleration

TL;DR

This paper investigates how non-minimal couplings of scalar fields to curvature or matter influence late-time cosmic acceleration, showing that curvature coupling naturally leads to de Sitter expansion regardless of potential steepness.

Contribution

It demonstrates that curvature coupling induces de Sitter expansion in scalar field models, extending understanding of late-time acceleration beyond minimal coupling scenarios.

Findings

Curvature coupling results in asymptotic de Sitter expansion.

Matter coupling does not significantly alter late-time dynamics.

Results generalize cosmic no-hair theorems for non-minimal couplings.

Abstract

Spatially homogeneous models with a scalar field non-minimally coupled to the space-time curvature or to the ordinary matter content are analysed with respect to late-time asymptotic behaviour, in particular to accelerated expansion and isotropization. It is found that a direct coupling to the curvature leads to asymptotic de Sitter expansion in arbitrary exponential potentials, thus yielding a positive cosmological constant although none is apparent in the potential. This holds true regardless of the steepness of the potential or the smallness of the coupling constant. For matter-coupled scalar fields, the asymptotics are obtained for a large class of positive potentials, generalizing the well-known cosmic no-hair theorems for minimal coupling. In this case it is observed that the direct coupling to matter does not impact the late-time dynamics essentially.