Observational Constraints on Gauge Field Production in Axion Inflation

TL;DR

This paper investigates how gauge field production during axion inflation affects observable signals in the CMB, providing constraints on the model from current data and exploring implications for non-Gaussianity.

Contribution

It compares observational constraints on gauge field production in axion inflation models using CMB data and discusses potential signatures of massive gauge fields.

Findings

CMB power spectrum constrains gauge field coupling strength.

Non-Gaussianity from inverse-decay is a weaker but relevant constraint.

Massive gauge fields can produce observable local non-Gaussianity.

Abstract

Models of axion inflation are particularly interesting since they provide a natural justification for the flatness of the potential over a super-Planckian distance, namely the approximate shift-symmetry of the inflaton. In addition, most of the observational consequences are directly related to this symmetry and hence are correlated. Large tensor modes can be accompanied by the observable effects of a the shift-symmetric coupling $\phi F\tilde F$ to a gauge field. During inflation this coupling leads to a copious production of gauge quanta and consequently a very distinct modification of the primordial curvature perturbations. In this work we compare these predictions with observations. We find that the leading constraint on the model comes from the CMB power spectrum when considering both WMAP 7-year and ACT data. The bispectrum generated by the non-Gaussian inverse-decay of the gauge field leads to a comparable but slightly weaker constraint. There is also a constraint from mu-distortion using TRIS plus COBE/FIRAS data, but it is much weaker. Finally we comment on a generalization of the model to massive gauge fields. When the mass is generated by some light Higgs field, observably large local non-Gaussianity can be produced.