Untangling features in the primordial spectra

Abstract

We discuss the possible existence of features in both the primordial power spectrum and bispectrum generated during a stage of single eld cosmic in ation. 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 in ation. The former are known to be produced by heavy elds, when the in ationary background trajectory in eld space undergoes a bend, whereas the latter are known to be produced by features in the in aton potential encountered as the in aton eld 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.