On the importance of heavy fields in pseudo-scalar inflation

TL;DR

This paper explores how heavy fields in effective field theory influence pseudo-scalar inflation, affecting curvature fluctuations and non-Gaussianity, especially when heavy field masses approach the Hubble scale.

Contribution

It introduces the effects of integrated heavy fields on pseudo-scalar inflation, highlighting their impact on dispersion relations and non-Gaussianity predictions.

Findings

Heavy fields alter the dispersion regime of curvature fluctuations.

Heavy fields coupled to Chern-Simons terms induce additional operators.

Significance increases as heavy field mass approaches the Hubble scale.

Abstract

Pseudo-scalar inflation coupled with U(1) gauge fields through the Chern-Simons term has been extensively studied. However, new physics arising from UV theories may still influence the pseudo-scalar field at low-energy scales, potentially impacting predictions of inflation. In the realm of effective field theory (EFT), we investigated axion inflation, where operators from heavy fields are also present, in addition to the axion and gauge fields. The integrated out fields have two significant effects: the non-linear dispersion regime and coupling heavy modes to the Chern-Simons term. The first effect changes the propagation of the curvature fluctuation, while the second one results in additional operators that contribute to curvature fluctuation via inverse decay. We derived the power spectrum and magnitude of equilateral non-Gaussianity in this low-energy EFT. We found that the second effect could become significant as the mass of heavy fields approaches Hubble scale.