Cosmological dynamics of Scalar--Tensor Gravity

TL;DR

This paper analyzes the phase-space dynamics of Scalar--Tensor Gravity models with specific coupling and potential forms, revealing mechanisms for evolution towards General Relativity, accelerated expansion, and inflationary phases.

Contribution

It provides a detailed phase-space analysis of Scalar--Tensor Gravity with quadratic coupling and power-law potential, uncovering evolution pathways and stability properties.

Findings

Evolution towards GR depends on potential form

Transient accelerated expansion phases identified

Unstable inflationary phases can become stable

Abstract

We study the phase--space of FLRW models derived from Scalar--Tensor Gravity where the non--minimal coupling is $F(\phi)=\xi\phi^2$ and the effective potential is $V(\phi)=\lambda \phi^n$. Our analysis allows to unfold many feature of the cosmology of this class of theories. For example, the evolution mechanism towards states indistinguishable from GR is recovered and proved to depend critically on the form of the potential $V(\phi)$. Also, transient almost--Friedmann phases evolving towards accelerated expansion and unstable inflationary phases evolving towards stable ones are found. Some of our results are shown to hold also for the String-Dilaton action.