Oscillating Chiral Tensor Spectrum from Axionic Inflation
  We study the axionic inflation with a modulated potential and examine if the
primordial tensor power spectrum exhibits oscillatory feature, which is
testable with future space-based gravitational wave experiments such as DECIGO
and BBO. In the case of the single-field axion monodromy inflation, it turns
out that it is difficult to detect the oscillation in the spectrum due to
suppression of the sub-Planckian decay constant of axion. On the other hand, in
the case of aligned chromo-natural inflation where the axion is coupled to a
SU(2) gauge field, it turns out that the sizable oscillation in the tensor
spectrum can occur due to the enhancement of chiral gravitational waves sourced
by the gauge field. We expect that this feature will be a new probe to axion
phenomenologies in early universe through the chiral gravitational waves.
