Primordial Gravitational Waves Induced by Magnetic Fields in an Ekpyrotic Scenario

TL;DR

This paper demonstrates that primordial gravitational waves can be generated in ekpyrotic scenarios via gauge fields, challenging the notion that their detection distinguishes inflation from ekpyrosis, with scalar fluctuations remaining negligible.

Contribution

It shows that gauge fields can source detectable gravitational waves in ekpyrotic models, providing a new way to differentiate cosmological scenarios.

Findings

Primordial gravitational waves can be produced in ekpyrotic models via gauge fields.

Scalar fluctuations sourced by gauge fields are negligible in ekpyrotic scenarios.

Detection of such gravitational waves does not necessarily distinguish inflation from ekpyrosis.

Abstract

Both inflationary and ekpyrotic scenarios can account for the origin of the large scale structure of the universe. It is often said that detecting primordial gravitational waves is the key to distinguish both scenarios. We show that this is not true if the gauge kinetic function is present in the ekpyrotic scenario. In fact, primordial gravitational waves sourced by the gauge field can be produced in an ekpyrotic universe. We also study scalar fluctuations sourced by the gauge field and show that it is negligible compared to primordial gravitational waves. This comes from the fact that the fast roll condition holds in ekpyrotic models.