Higgsed Chromo-Natural Inflation

TL;DR

This paper shows that breaking the SU(2) gauge symmetry in Chromo-Natural Inflation makes it compatible with observations, producing detectable chiral gravitational waves at sub-GUT energy scales.

Contribution

It introduces a mechanism to reconcile Chromo-Natural Inflation with data by spontaneous symmetry breaking, enabling observable gravitational waves with sub-Planckian fields.

Findings

Negligible isocurvature perturbations.

Chiral gravitational waves with r~10^{-3} can be generated.

Gravitational wave spectrum can be blue or red tilted.

Abstract

We demonstrate that Chromo-Natural Inflation can be made consistent with observational data if the SU(2) gauge symmetry is spontaneously broken. Working in the Stueckelberg limit, we show that isocurvature is negligible, and the resulting adiabatic fluctuations can match current observational constraints. Observable levels of chirally-polarized gravitational radiation ($r\sim 10^{-3}$) can be produced while the evolution of all background fields is sub-Planckian. The gravitational wave spectrum is amplified via linear mixing with the gauge field fluctuations, and its amplitude is not simply set by the Hubble rate during inflation. This allows observable gravitational waves to be produced for an inflationary energy scale below the GUT scale. The tilt of the resulting gravitational wave spectrum can be either blue or red.