Untangling features in the primordial spectra
  We discuss the possible existence of features in both the primordial power
spectrum and bispectrum generated during a stage of single field cosmic
inflation. We argue that there are two main classes of features: those produced
by a sudden time variation of the sound speed of curvature perturbations, and
those produced by a sudden change in the expansion rate during inflation. The
former are known to be produced by heavy fields, when the inflationary
background trajectory in field space undergoes a bend, whereas the latter are
known to be produced by features in the inflaton potential encountered as the
inflaton field descends its slope. In general, features are expected to be the
result of these two sources combined, however, it is possible that one source
dominated over the other, resulting in a distinctive pattern that may be
observationally tested. We deduce a relation that gives us the shape of
features in the bispectrum provided that we know the shape of features in the
power spectrum, and show that each one of these two classes of features leaves
a particular footprint in the distribution of perturbations that could be
uncovered by a joint analysis of the primordial power spectrum and bispectrum.
