Gauge Field Production in Axion Inflation: Consequences for Monodromy,
  non-Gaussianity in the CMB, and Gravitational Waves at Interferometers
  Models of inflation based on axions, which owe their popularity to the
robustness against UV corrections, have also a very distinct class of
signatures. The relevant interactions of the axion are a non-perturbative
oscillating contribution to the potential and a shift-symmetric coupling to
gauge fields. We review how these couplings affect the cosmological
perturbations via a unified study based on the in-in formalism. We then note
that, when the inflaton coupling to gauge fields is high enough to lead to
interesting observational results, the backreaction of the produced gauge
quanta on the inflaton dynamics becomes relevant during the final stage of
inflation, and prolongs its duration by about 10 e-foldings. We extend existing
results on gravity wave production in these models to account for this late
inflationary phase. The strong backreaction phase results in an enhancement of
the gravity wave signal at the interferometer scales. As a consequence, the
signal is potentially observable at Advanced LIGO/VIRGO for the most natural
duration of inflation in such models. Finally, we explicitly compute the axion
couplings to gauge fields in string theory construction of axion monodromy
inflation and identify cases where they can trigger interesting
phenomenological effects.
