Oscillatory features in the curvature power spectrum after a sudden turn of the inflationary trajectory

TL;DR

This paper analyzes how sharp turns in two-field inflation affect the curvature power spectrum, focusing on resonant effects from background oscillations and mode couplings, providing analytical estimates and confirming previous results.

Contribution

It offers an analytical estimate of resonant effects and mode couplings in two-field inflation after a sharp turn, refining previous amplitude predictions.

Findings

Resonant effects have the same spectral dependence but smaller amplitude than earlier estimates.

Direct coupling between modes at the turn confirms previous results.

Analytical approach in the mass basis enhances understanding of inflationary perturbations.

Abstract

In the context of two-field inflation characterized by a light direction and a heavy direction, we revisit the question of the impact of the massive modes on the power spectrum produced after a turn in the inflationary trajectory. We consider in particular the resonant effect due to the background oscillations following a sharp turn. Working in the mass basis, i.e. in the basis spanned by the eigenvectors of the effective mass matrix for the perturbations, we provide an analytical estimate of the resonant effect, using the in-in formalism. In comparison with earlier estimates, we find the same the spectral dependence but a smaller amplitude. We also compute, again via the in-in formalism, the effect of the direct coupling between the light and heavy modes at the instant of the turn and confirm our previous results obtained via a different method.