Cosmological solutions of time varying speed of light theories

TL;DR

This paper explores scalar-tensor theories with a varying speed of light in flat FRW cosmology, deriving exact solutions and analyzing their dynamics to understand conditions for attractors and horizon criteria.

Contribution

It provides new exact solutions and dynamical analysis of varying speed of light theories in both metric and Palatini formalisms, highlighting the quadratic form of the coupling coefficient.

Findings

Attractors have a quadratic non-minimal coupling coefficient.

Only de Sitter attractors satisfy horizon criteria.

Exact solutions are found in both formalisms.

Abstract

We consider scalar-tensor theory for describing varying speed of light in a spatially flat FRW space-time. We find some exact solutions in the metric and Palatini formalisms. Also we examine the dynamics of this theory by dynamical system method assuming a $\Lambda$CDM background and we find some exact solutions by considering the character of critical points of the theory in both formalisms. We show that for any attractor the form of non-minimal coupling coefficient is quadratic in terms of the scalar field $\Psi$. Also we show that only attractors of the de Sitter era satisfy the horizon criteria.