Gravity waves and non-Gaussian features from particle production in a
  sector gravitationally coupled to the inflaton
  We study the possibility that particle production during inflation could
source observable gravity waves on scales relevant for Cosmic Microwave
Background experiments. A crucial constraint on such scenarios arises because
particle production can also source inflaton perturbations, and might ruin the
usual predictions for a nearly scale invariant spectrum of nearly Gaussian
curvature fluctuations. To minimize this effect, we consider two models of
particle production in a sector that is only gravitationally coupled to the
inflaton. For a single instantaneous burst of massive particle production, we
find that localized features in the scalar spectrum and bispectrum might be
observable, but gravitational wave signatures are unlikely to be detectable
(due to the suppressed quadrupole moment of non-relativistic quanta) without
invoking some additional effects. We also consider a model with a rolling
pseudoscalar that leads to a continuous production of relativistic gauge field
fluctuations during inflation. Here we find that gravitational waves from
particle production can actually exceed the usual inflationary vacuum
fluctuations in a regime where non-Gaussianity is consistent with observational
limits. In this model observable B-mode polarization can be obtained for any
choice of inflaton potential, and the amplitude of the signal is not
necessarily correlated with the scale of inflation.
