Perturbation Theory in k-Inflation Coupled to Matter

TL;DR

This paper investigates how abrupt changes in the coupling function in k-inflation models affect the curvature perturbation power spectrum, revealing modifications to inflationary predictions and potential observational signatures.

Contribution

It introduces a scalar-tensor extension of k-inflation with matter coupling and derives a modified Mukhanov-Sasaki equation accounting for abrupt coupling changes.

Findings

Significant corrections to the power spectrum occur with abrupt coupling changes.

The model modifies Starobinsky's perturbation features.

Infrared power spectrum is altered by these features.

Abstract

We consider k-inflation models where the action is a non-linear function of both the inflaton and the inflaton kinetic term. We focus on a scalar-tensor extension of k-inflation coupled to matter for which we derive a modified Mukhanov-Sasaki equation for the curvature perturbation. Significant corrections to the power spectrum appear when the coupling function changes abruptly along the inflationary trajectory. This gives rise to a modification of Starobinsky's model of perturbation features. We analyse the way the power spectrum is altered in the infrared when such features are present.