Phenomenology of fermion production during axion inflation
  We study the production of fermions through a derivative coupling with a
pseudoscalar inflaton and the effects of the produced fermions on the scalar
primordial perturbations. We present analytic results for the modification of
the scalar power spectrum due to the produced fermions, and we estimate the
amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we
find a regime where the effect of the fermions gives the dominant contribution
to the scalar spectrum while the amplitude of the bispectrum is small and in
agreement with observation. We also note the existence of a regime in which the
backreaction of the fermions on the evolution of the zero-mode of the inflaton
can lead to inflation even if the potential of the inflaton is steep and does
not satisfy the slow-roll conditions.
