Sudden variations in the speed of sound during inflation: features in the power spectrum and bispectrum

TL;DR

This paper investigates how sudden changes in the speed of sound during inflation create high-frequency oscillations in the power spectrum and bispectrum, affecting observable features in primordial fluctuations.

Contribution

It introduces a formalism using effective field theory to analyze the impact of abrupt sound speed variations on inflationary perturbations and their statistical signatures.

Findings

Oscillations in the power spectrum persist at large momenta.

Bispectrum amplitude diverges for very short duration changes.

Features depend on the duration of the sound speed change.

Abstract

We employ the formalism of the effective field theory of inflation to study the effects of a sudden change in the speed of sound of the inflationary perturbations. Such an event generates a feature with high frequency oscillations both in the two- and in the three-point functions of the curvature fluctuations. We study, at first order in the magnitude of the change of the speed of sound, the dependence of the power spectrum and of the bispectrum on the duration of the change. In the limit of a very short duration, the oscillations in the power spectrum persist up to very large momenta and the amplitude of the feature in the bispectrum diverges while its location moves to increasing momenta.