The Effective Field Theory of Inflation Models with Sharp Features
  We describe models of single-field inflation with small and sharp step
features in the potential (and sound speed) of the inflaton field, in the
context of the Effective Field Theory of Inflation. This approach allows us to
study the effects of features in the power-spectrum and in the bispectrum of
curvature perturbations, from a model-independent point of view, by
parametrizing the features directly with modified "slow-roll" parameters. We
can obtain a self-consistent power-spectrum, together with enhanced
non-Gaussianity, which grows with a quantity $\beta$ that parametrizes the
sharpness of the step. With this treatment it is straightforward to generalize
and include features in other coefficients of the effective action of the
inflaton field fluctuations. Our conclusion in this case is that, excluding
extrinsic curvature terms, the only interesting effects at the level of the
bispectrum could arise from features in the first slow-roll parameter
$\epsilon$ or in the speed of sound $c_s$. Finally, we derive an upper bound on
the parameter $\beta$ from the consistency of the perturbative expansion of the
action for inflaton perturbations. This constraint can be used for an
estimation of the signal-to-noise ratio, to show that the observable which is
most sensitive to features is the power-spectrum. This conclusion would change
if we consider the contemporary presence of a feature and a speed of sound $c_s
< 1$, as, in such a case, contributions from an oscillating folded
configuration can potentially make the bispectrum the leading observable for
feature models.
