Tensor Spectra Templates for Axion-Gauge Fields Dynamics during Inflation

Abstract

$SU(2)$ gauge fields can generate large gravitational waves during inflation, if they are coupled to an axion which can be either the inflaton or a spectator field. The shape of the produced tensor power spectrum ${\mathcal{P}}_h$ depends on the form of the axion potential. We derive analytic expressions and provide general templates for ${\mathcal{P}}_h$ for various types of the spectator axion potential. Furthermore, we explore the detectability of the oscillatory feature, which is present in ${\mathcal{P}}_h$ in the case of an axion monodromy model, by possible future CMB B-mode polarization observations.

Comments: 31 pages, 11 figures