Chiral gravitational waves from axion-inflation models with step-like features

Models with an axion-like inflaton have received considerable attention since the early 90’s, since pseudo-Nambu Goldstone bosons (pNGBs) have a radiatively stable potential and they are abundant in string theory. In these models, the inflaton can be coupled with a gauge field, leading to a rich phenomenology. The produced gauge quanta source the scalar and tensor components of the metric perturbations, with the latter giving rise to non-vanishing TB and EB correlation functions in the Cosmic Microwave Background (CMB), which can be detected by ongoing and future experiments. In this work, we study the dynamics of axion-inflation models, both analytically and numerically, focusing mainly on chiral gravitational waves that are generated in three different scenarios: natural inflation, axion monodromy and a linear potential with a step-like feature. We find that a signal can be detected by LISA and by advanced LIGO and Einstein Telescope if the step is broad or very steep, respectively, but in these cases problems related to strong backreaction on Friedmann equation might arise. If instead the step is just a small correction to the linear potential, chiral gravitational waves might be detected by LISA in a weak backreaction regime.