Higgsed Chromo-Natural Inflation
  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. 
Peter Adshead, Emil Martinec, Evangelos I. Sfakianakis, and Mark Wyman
hep-th astro-ph.CO