Resonant features in the stochastic gravitational wave background
  We analyse the post-inflationary contribution to the stochastic gravitational
wave background due to a resonant feature in the scalar power spectrum, which
is characterised by an oscillation in $\log(k)$, complementing our previous
work arXiv:2012.02761 on sharp features. Primordial features signal departures
of inflation from the single-field slow-roll paradigm and are motivated by
embeddings of inflation in high energy physics. We find that the oscillation in
the scalar power spectrum leads to a corresponding modulation in the
gravitational wave spectrum that can be understood as a superposition of two
oscillatory pieces, one with the original frequency of the scalar oscillations,
and one with double frequency. For oscillations with slowly-varying amplitude
this oscillatory part can be computed semi-analytically. Our results can be
used as templates for the reconstruction of the signal from future data and
permit extracting information about the small scale scalar power spectrum from
measurements of the stochastic gravitational wave background.
