Primordial gravitational waves for universality classes of pseudoscalar inflation

TL;DR

This paper explores how pseudoscalar inflation models can produce detectable primordial gravitational waves through gauge field couplings, offering new observational avenues beyond traditional CMB bounds.

Contribution

It introduces a framework linking pseudoscalar inflation to observable gravitational wave signatures across multiple frequency bands, especially highlighting Starobinsky inflation.

Findings

Pseudoscalar couplings can generate detectable GW signals.

Multi-frequency GW detection can probe inflationary microphysics.

Starobinsky inflation shows promising observational signatures.

Abstract

Current bounds from the polarization of the CMB predict the scale-invariant gravitational wave (GW) background of inflation to be out of reach for upcoming GW interferometers. This prospect dramatically changes if the inflaton is a pseudoscalar, in which case its generic coupling to any abelian gauge field provides a new source of GWs, directly related to the dynamics of inflation. This opens up new ways of probing the scalar potential responsible for cosmic inflation. Dividing inflation models into universality classes, we analyze the possible observational signatures. One of the most promising scenarios is Starobinsky inflation, which may lead to observational signatures both in direct GW detection as well as in upcoming CMB detectors. In this case, the complementarity between the CMB and direct GW detection, as well as the possibility of a multi-frequency analysis with upcoming ground and space based GW interferometers, may provide a first clue to the microphysics of inflation.