Natural inflation, strong dynamics, and the role of generalized anomalies

TL;DR

This paper revisits natural inflation models, showing the breakdown of single-field effective theory during large-field excursions and proposing a modified potential that incorporates heavy degrees of freedom through a gauge theory framework, with implications for multi-field inflation dynamics and observational consistency.

Contribution

It introduces a gauge theory embedding to account for heavy hadrons affecting inflation, and analyzes multi-field inflation dynamics with observational implications.

Findings

Single-field effective theory breaks down during large excursions.

Modified potential accounts for heavy hadrons and their impact.

Conditions for successful inflation consistent with CMB data.

Abstract

We revisit models of natural inflation and show that the single-field effective theory described by the potential $V(a)\sim \cos\frac{a}{f}$ breaks down as the inflaton $a$ makes large-field excursions, even for values of $f$ smaller than the Planck scale. In order to remedy the problem, we modify the potential in order to account for the heavy degrees of freedom (hadrons) that become intertwined with the light inflaton as the latter rolls down its potential. By embedding the low energy degrees of freedom into an ultraviolet complete gauge theory, we argue that the intertwining between the two scales can be explained as the result of a generalized mixed 't Hooft anomaly between the discrete chiral symmetry and background fractional fluxes in the baryon number, color, and flavor directions. Further, we study the multi-field inflation and show that it entertains rich dynamics. Inflating near the hilltop excites the hadrons and spoils the slow-roll parameters, in contradistinction with the expectations in the single-field inflation. Nevertheless, we identify a safe zone where inflation can proceed successfully. We determine the conditions under which the Universe inflates by at least $60$ e-foldings and inflation leads to a power spectrum and tensor to scalar ratio that are consistent with the Cosmic Microwave Background data.