On gravitational waves in Born-Infeld inspired non-singular cosmologies

TL;DR

This paper investigates gravitational wave behavior in non-singular cosmologies inspired by Born-Infeld gravity, highlighting stability differences between bouncing and Minkowski solutions and their implications for early universe models.

Contribution

It provides a detailed analysis of gravitational wave propagation, stability, and instabilities in Born-Infeld inspired non-singular cosmologies, extending to more general theories.

Findings

Bouncing solutions are more prone to instabilities.

Asymptotically Minkowski solutions can be stabilized.

Gravitational wave behavior is influenced by matter sound speed.

Abstract

We study the evolution of gravitational waves for non-singular cosmological solutions within the framework of Born-Infeld inspired gravity theories, with special emphasis on the Eddington-inspired Born-Infeld theory. We review the existence of two types of non-singular cosmologies, namely bouncing and asymptotically Minkowski solutions, from a perspective that makes their features more apparent. We study in detail the propagation of gravitational waves near these non-singular solutions and carefully discuss the origin and severity of the instabilities and strong coupling problems that appear. We also investigate the role of the adiabatic sound speed of the matter sector in the regularisation of the gravitational waves evolution. We extend our analysis to more general Born-Infeld inspired theories where analogous solutions are found. As a general conclusion, we obtain that the bouncing solutions are generally more prone to instabilities, while the asymptotically Minkowski solutions can be rendered stable, making them appealing models for the early universe.