Axion inflation with cross-correlated axion isocurvature perturbations

TL;DR

This paper explores axion-based inflation models within superstring theory, focusing on the generation and correlation of adiabatic and isocurvature perturbations, and compares their compatibility with Planck data.

Contribution

It introduces a framework for calculating cross-correlations between adiabatic and isocurvature modes in string axion inflation models.

Findings

Correlated isocurvature modes are favored in axion monodromy inflation.

Natural inflation disfavors the existence of such correlated isocurvature modes.

Concrete examples demonstrate how string axion couplings lead to these correlations.

Abstract

We study the inflation scenarios, in the framework of superstring theory, where the inflaton is an axion producing the adiabatic curvature perturbations while there exists another light axion producing the isocurvature perturbations. We discuss how the non-trivial couplings among string axions can generically arise, and calculate the consequent cross-correlations between the adiabatic and isocurvature modes through concrete examples. Based on the Planck analysis on the generally correlated isocurvature perturbations, we show that there is a preference for the existence of the correlated isocurvature modes for the axion monodromy inflation while the natural inflation disfavors such isocurvature modes.