Chromo-Natural Inflation in the Axiverse

TL;DR

This paper explores a hybrid inflation model involving two axions and an SU(2) gauge field, showing how natural inflation transitions to chromo-natural inflation, producing potentially observable chiral gravitational waves.

Contribution

It introduces a novel two-axion model with a gauge field that transitions from natural to chromo-natural inflation, predicting detectable gravitational waves.

Findings

Natural inflation lasts for tens of e-foldings before chromo-natural inflation begins.

The model predicts chiral gravitational waves in the high-frequency range.

Predictions align with CMB observations on large scales.

Abstract

We study chromo-natural inflation in the axiverse. More precisely, we investigate natural inflation with two axions coupled with a SU(2) gauge field. Assuming a hierarchy between the coupling constants, we find that for certain initial conditions, conventional natural inflation commences and continues for tens of e-foldings, and subsequently chromo-natural inflation takes over from natural inflation. For these solutions, we expect that the predictions are in agreement with observations on CMB scales. Moreover, since chromo-natural inflation occurs in the latter part of the inflationary stage, chiral primordial gravitational waves are produced in the interesting frequency range higher than $10^{-10}$Hz, which might be detectable by future gravitational wave observations.