Sudden variations in the speed of sound during inflation: features in
  the power spectrum and bispectrum
  We employ the formalism of the effective field theory of inflation to study
the effects of a sudden change in the speed of sound of the inflationary
perturbations. Such an event generates a feature with high frequency
oscillations both in the two- and in the three-point functions of the curvature
fluctuations. We study, at first order in the magnitude of the change of the
speed of sound, the dependence of the power spectrum and of the bispectrum on
the duration of the change. In the limit of a very short duration, the
oscillations in the power spectrum persist up to very large momenta and the
amplitude of the feature in the bispectrum diverges while its location moves to
increasing momenta.
