Low-Energy Effective Field Theory for Chromo-Natural Inflation

TL;DR

This paper derives a low-energy effective field theory for chromo-natural inflation, showing it can be described by a single scalar field with a non-minimal kinetic term, simplifying analysis and confirming its stability and viability.

Contribution

It introduces a precise effective theory for chromo-natural inflation, demonstrating the decoupling of gauge fields and the applicability of a P(X,χ) model for analysis.

Findings

Effective single scalar field description derived

Gauge field fluctuations are heavy and decouple during inflation

Chromo-natural inflation is stable and viable for perturbation generation

Abstract

Chromo-natural inflation is a novel model of inflation which relies on the existence of non-abelian gauge fields interacting with an axion. In its simplest realization, an SU(2) gauge field is assumed to begin inflation in a rotationally invariant VEV. The dynamics of the gauge fields significantly modifies the equations of motion for the axion, providing an additional damping term that supports slow-roll inflation, without the need to fine tune the axion decay constant. We demonstrate that in an appropriate slow-roll limit it is possible to integrate out the massive gauge field fluctuations whilst still maintaining the nontrivial modifications of the gauge field to the axion. In this slow-roll limit, chromo-natural inflation is exactly equivalent to a single scalar field effective theory with a non-minimal kinetic term, i.e. a P(X,\chi) model. This occurs through a precise analogue of the gelaton mechanism, whereby heavy fields can have unsuppressed effects on the light field dynamics without contradicting decoupling. The additional damping effect of the gauge fields can be completely captured by the non-minimal kinetic term of the single scalar field effective theory. We utilize the single scalar field effective theory to infer the power spectrum and non-gaussianities in chromo-natural inflation and confirm that the mass squared of all the gauge field fluctuations is sufficiently large and positive that they completely decouple during inflation. These results confirm that chromo-natural inflation is a viable, stable and compelling model for the generation of inflationary perturbations.