Linear perturbations in Eddington-inspired Born-Infeld gravity

TL;DR

This paper investigates the stability of linear perturbations in Eddington-inspired Born-Infeld gravity, revealing mode stability depends on the sign of the parameter and wave vector, with implications for the theory's viability.

Contribution

It provides a detailed analysis of linear perturbations and their stability in Eddington-inspired Born-Infeld gravity, highlighting mode behaviors across different regimes and parameter signs.

Findings

Scalar modes stable at infinite wavelength for positive κ

Vector modes are stable in the Eddington regime

Tensor modes are unstable regardless of wave vector for positive κ

Abstract

We study the full linear perturbations of a homogeneous and isotropic spacetime in the Eddington-inspired Born-Infeld gravity. The stability of the perturbations are analyzed in the Eddington regime. We find that, for positive $\kappa$, the scalar modes are stable in the infinite wavelength limit ($k=0$) but unstable for $k\neq0$. The vector modes are stable and the tensor mode is unstable in the Eddington regime, independent of the wave vector $k$. However, these modes are unstable and hence cause the instabilities for negative $\kappa$.