Flattened Axion Monodromy Beyond Two Derivatives

TL;DR

This paper investigates string-inspired two-field axion monodromy inflation models with a heavy modulus, revealing how backreaction effects influence the scalar potential, non-Gaussianity, and inflationary observables.

Contribution

It introduces two effective field theories capturing backreaction effects of heavy moduli in axion monodromy inflation, including potential flattening and non-Gaussianity.

Findings

Heavy moduli induce non-Gaussianity in inflationary perturbations.

Backreaction effects modify the spectral index and tensor-to-scalar ratio.

Two equivalent EFTs describe the impact of heavy moduli on inflation dynamics.

Abstract

We study string inspired two-field models of large-field inflation based on axion monodromy in the presence of an interacting heavier modulus. This class of models has enough structure to approximate at least part of the backreaction effects known in full string theory, such as kinetic mixing with the axion, and flattening of the scalar potential. Yet, it is simple enough to fully describe the structure of higher-point curvature perturbation interactions driven by the adjusting modulus backreaction dynamics. We find that the presence of the heavy modulus can be described via two equivalent effective field theories, both of which can incorporate reductions of the speed of sound. Hence, the presence of heavier moduli in axion monodromy inflation constructions will necessarily generate some amount of non-Gaussianity accompanied by changes to $n_s$ and $r$ beyond what results from just from the well known adiabatic flattening backreaction.