Non-singular Universes a la Palatini

TL;DR

This paper explores how generalized Palatini f(R) theories with quadratic Ricci tensor terms can produce non-singular bouncing cosmological solutions, including in anisotropic models, extending previous work on singularity avoidance.

Contribution

It introduces more general actions with quadratic Ricci tensor terms in Palatini formalism, leading to richer bouncing cosmologies, even in anisotropic scenarios.

Findings

Quadratic Ricci tensor terms enable bouncing solutions in anisotropic models.

Generalized actions produce a richer phenomenology than simpler f(R) models.

Bouncing solutions are consistent with non-singular universe scenarios.

Abstract

It has recently been shown that f(R) theories formulated in the Palatini variational formalism are able to avoid the big bang singularity yielding instead a bouncing solution. The mechanism responsible for this behavior is similar to that observed in the effective dynamics of loop quantum cosmology and an f(R) theory exactly reproducing that dynamics has been found. I will show here that considering more general actions, with quadratic contributions of the Ricci tensor, results in a much richer phenomenology that yields bouncing solutions even in anisotropic (Bianchi I) scenarios. Some implications of these results are discussed.