Bouncing Universes in Scalar-Tensor Gravity Around Conformal Invariance

TL;DR

This paper explores how scalar-tensor gravity models can produce bouncing universes, especially when the scalar field's coupling to gravity slightly deviates from conformal invariance, revealing new dynamical features.

Contribution

It demonstrates the existence of bouncing universe solutions in scalar-tensor gravity with nonconformal coupling, including numerical analysis of deviations and novel behaviors.

Findings

Bouncing universes exist with slight deviations from conformal coupling.

Solutions can leave the effective phantom regime.

Numerical evidence supports the robustness of bouncing solutions.

Abstract

We consider the possibility to produce a bouncing universe in the framework of scalar-tensor gravity when the scalar field has a nonconformal coupling to the Ricci scalar. We prove that bouncing universes regular in the future with essentially the same dynamics as for the conformal coupling case do exist when the coupling deviates slightly from it. This is found numerically for more substantial deviations as well. In some cases however new features are found like the ability of the system to leave the effective phantom regime.