Cosmology with Eddington-inspired Gravity

TL;DR

This paper investigates the cosmological dynamics under Eddington-inspired gravity, revealing singularity avoidance, oscillatory behaviors, and novel expansion patterns depending on the parameter  and matter content.

Contribution

It extends previous work by analyzing various matter fields and spatial curvature effects within Eddington-inspired gravity, highlighting new cosmological behaviors and conditions for singularity avoidance.

Findings

Singularity avoidance for  > 0 with perfect fluids and scalar fields.

Oscillations between finite densities for  < 0 with spatial curvature.

Multiple sign changes in expansion rate before GR-like behavior.

Abstract

We study the dynamics of homogeneous, isotropic universes which are governed by the Eddington-inspired alternative theory of gravity which has a single extra parameter, $\kappa$. Previous results showing singularity-avoiding behaviour for $\kappa > 0$ are found to be upheld in the case of domination by a perfect fluid with equation of state parameter $w > 0$. The range $-1/3 < w < 0$ is found to lead to universes which experience unbounded expansion rate whilst still at a finite density. In the case $\kappa < 0$ the addition of spatial curvature is shown to lead to the possibility of oscillation between two finite densities. Domination by a scalar field with an exponential potential is found to also lead to singularity-avoiding behaviour when $\kappa > 0$. Certain values of the parameters governing the potential lead to behaviour in which the expansion rate of the universe changes sign several times before transitioning to regular GR-like behaviour.