Cosmological singularities in Eddington-inspired-Born-Infeld theory and its possible extension

TL;DR

This paper explores how Eddington-inspired-Born-Infeld (EiBI) gravity can alleviate various cosmological singularities and introduces an extension of the theory that allows for bounces and inflationary phases.

Contribution

It analyzes the singularity-avoidance capabilities of EiBI gravity and proposes a generalized model with added terms that enable bounces and inflation.

Findings

Most singularities can be partially alleviated in EiBI model.

Adding a trace term allows for bounces and smoother singularities.

Certain parameters enable a big bang followed by inflation.

Abstract

The Eddington-inspired-Born-Infeld (EiBI) gravity, which is formulated within the Palatini formalism, is characterized by its ability to cure the big bang singularity in the very beginning of the Universe. We further analyze the EiBI phantom model, and investigate the possible avoidance or alleviation of other dark energy related singularities. We find that except for the big rip singularity and little rip event, most of the cosmological singularities of interest can be partially alleviated in this model. Furthermore, we generalize the EiBI theory by adding a pure trace term to the determinant of the action. This amendment is the most general rank-two tensor composed of up to first order of the Riemann curvature. We find that this model allows the occurrence of primitive bounces and some smoother singularities than that of big bang. Most interestingly, for certain parameter space, the big bang singularity can be followed naturally by an inflationary stage in a radiation dominated universe.