A tensor instability in the Eddington inspired Born-Infeld Theory of Gravity

TL;DR

This paper investigates tensor perturbations in an extended Eddington-inspired Born-Infeld gravity, revealing a linear instability in the tensor modes during the strong gravity regime, with significant cosmological implications.

Contribution

It identifies a tensor instability in the Eddington regime of the extended theory, highlighting potential issues for its cosmological viability.

Findings

Tensor modes are linearly unstable in the Eddington regime.

The instability occurs deep within the strong gravity regime.

Implications for cosmological models based on this theory are discussed.

Abstract

In this paper we consider an extension to Eddington's proposal for the gravitational action. We study tensor perturbations of a homogeneous and isotropic space-time in the Eddington regime, where modifications to Einstein gravity are strong. We find that the tensor mode is linearly unstable deep in the Eddington regime and discuss its cosmological implications.