Bounce and cyclic cosmology in new gravitational scalar-tensor theories

TL;DR

This paper explores bounce and cyclic cosmologies within new ghost-free scalar-tensor theories of gravity, deriving conditions for bounces and constructing specific Lagrangians to realize cyclic universe models.

Contribution

It introduces a class of ghost-free scalar-tensor theories with Ricci scalar derivatives, providing analytical bounce conditions and constructing Lagrangians for cyclic cosmologies.

Findings

Derived analytical bounce conditions.

Constructed Lagrangians for cyclic scale factors.

Identified qualitative behaviors for bounce realization.

Abstract

We study the bounce and cyclicity realization in the framework of new gravitational scalar-tensor theories. In these theories the Lagrangian contains the Ricci scalar and its first and second derivatives, in a specific combination that makes them free of ghosts, and transformed into the Einstein frame they are proved to be a subclass of bi-scalar extensions of general relativity. We present analytical expressions for the bounce requirements, and we examine the necessary qualitative behavior of the involved functions that can give rise to a given scale factor. Having in mind these qualitative forms, we reverse the procedure and we construct suitable simple Lagrangian functions that can give rise to a bounce or cyclic scale factor.