Oscillatory features in the curvature power spectrum after a sudden turn
  of the inflationary trajectory
  In the context of two-field inflation characterized by a light direction and
a heavy direction, we revisit the question of the impact of the massive modes
on the power spectrum produced after a turn in the inflationary trajectory. We
consider in particular the resonant effect due to the background oscillations
following a sharp turn. Working in the mass basis, i.e. in the basis spanned by
the eigenvectors of the effective mass matrix for the perturbations, we provide
an analytical estimate of the resonant effect, using the in-in formalism. In
comparison with earlier estimates, we find the same the spectral dependence but
a smaller amplitude. We also compute, again via the in-in formalism, the effect
of the direct coupling between the light and heavy modes at the instant of the
turn and confirm our previous results obtained via a different method.
