Bouncing Cosmologies in Palatini $f(R)$ Gravity

TL;DR

This paper explores how certain Palatini f(R) gravity models can produce non-singular bouncing cosmologies, replacing the Big Bang with a bounce, and discusses their potential to avoid singularities in stellar collapse.

Contribution

It demonstrates that specific Palatini f(R) models can generate bounce solutions without violating energy conditions, contrasting with traditional singular cosmologies.

Findings

Big Bang singularity can be replaced by a cosmic bounce.

Power-law Lagrangians with finite terms can lead to non-singular universes.

Models may also prevent singularities during stellar collapse.

Abstract

We consider the early time cosmology of f(R) theories in Palatini formalism and study the conditions that guarantee the existence of homogeneous and isotropic models that avoid the Big Bang singularity. We show that for such models the Big Bang singularity can be replaced by a cosmic bounce without violating any energy condition. In fact, the bounce is possible even for pressureless dust. We give a characterization of such models and discuss their dynamics in the region near the bounce. We also find that power-law lagrangians with a finite number of terms may lead to non-singular universes, which contrasts with the infinite-series Palatini f(R) lagrangian that one needs to fully capture the effective dynamics of Loop Quantum Cosmology. We argue that these models could also avoid the formation of singularities during stellar gravitational collapse.