The Behaviour Of Cosmological Models With Varying-G

TL;DR

This paper analyzes various cosmological models within scalar-tensor theories of gravity, exploring their solutions, behaviors, and constraints to understand universe evolution with a varying gravitational constant.

Contribution

It introduces a comprehensive set of exact solutions for different universe geometries in scalar-tensor theories, constrained by observational tests and exploring early and late-time dynamics.

Findings

Exact solutions for open, closed, and flat universes with matter and vacuum.

Conditions for bounce and expansion maxima in models.

Range of early and late-time behaviors identified.

Abstract

We provide a detailed analysis of Friedmann-Robertson-Walker universes in a wide range of scalar-tensor theories of gravity. We apply solution-generating methods to three parametrised classes of scalar-tensor theory which lead naturally to general relativity in the weak-field limit. We restrict the parameters which specify these theories by the requirements imposed by the weak-field tests of gravitation theories in the solar system and by the requirement that viable cosmological solutions be obtained. We construct a range of exact solutions for open, closed, and flat isotropic universes containing matter with equation of state $p\leq \frac{1}{3}\rho$ and in vacuum. We study the range of early and late-time behaviours displayed, examine when there is a `bounce' at early times, and expansion maxima in closed models.