Non-Gaussianity from Step Features in the Inflationary Potential
  We provide analytic solutions for the power spectrum and bispectrum of
curvature fluctuations produced by a step feature in the inflaton potential,
valid in the limit that the step is short and sharp. In this limit, the
bispectrum is strongly scale dependent and its effective non-linearity attains
a large oscillatory amplitude. The perturbations to the curvature power
spectrum, on the other hand, remain a small component on top of the usual
spectrum of fluctuations generated by slow roll. We utilize our analytic
solutions to assess the observability of the predicted non-Gaussian signatures
and show that, if present, only very sharp steps on scales larger than ~ 2 Gpc
are likely to be able to be detected by Planck. Such features are not only
consistent with WMAP7 data, but can also improve its likelihood by 2 Delta ln L
~ 12 for two extra parameters, the step location and height. If this
improvement were due to a slow roll violating step as considered here, a
bispectrum or corresponding polarization power spectrum detection would provide
definitive checks as to its primordial origin.
