Magnon Inflation: Slow Roll with Steep Potentials

TL;DR

This paper introduces multi-scalar effective field theories enabling slow inflation with steep potentials by dominated single-derivative kinetic terms, expanding the understanding of inflationary models beyond traditional slow-roll conditions.

Contribution

It develops a novel EFT framework with single-derivative kinetic terms for multi-scalar fields, capturing slow-roll inflation even with steep potentials, and relates it to UV theories like Chromo-natural inflation.

Findings

EFT achieves slow roll with steep potentials via single-derivative dominance.

The framework generalizes Cuscuton models to multiple fields.

A target-space 2-form, F_{ab}, introduces new slow-roll mechanisms.

Abstract

We find multi-scalar effective field theories (EFTs) that can achieve a slow inflationary roll despite having a scalar potential that does not satisfy the usual slow-roll condition (d V)^2 << V^2/Mp^2. They evade the usual slow-roll conditions on $V$ because their kinetic energies are dominated by single-derivative terms rather than the usual two-derivative terms. Single derivatives dominate during slow roll and so do not require a breakdown of the usual derivative expansion that underpins calculational control in much of cosmology. The presence of such terms requires some sort of UV Lorentz-symmetry breaking during inflation (besides the usual cosmological breaking). Chromo-natural inflation provides an example of a UV theory that can generate the multi-field single-derivative terms we consider, and we argue that the EFT we find indeed captures the slow-roll conditions for the background evolution for Chromo-natural inflation. We also show that our EFT can be understood as a multi-field generalization of the single-field Cuscuton models. The multi-field case introduces a new feature, however: the scalar kinetic terms define a target-space 2-form, F_{ab}, whose antisymmetry gives new ways for slow roll to be achieved.