The strong backreaction regime in axion inflation

TL;DR

This paper investigates the complex non-linear dynamics of axion inflation, revealing how inhomogeneities and strong backreaction influence inflation duration, oscillation behavior, and gauge field spectra, with implications for observable phenomena.

Contribution

It provides the first detailed analysis of inhomogeneous effects and full dynamical range during strong backreaction in axion inflation, extending beyond previous homogeneous models.

Findings

Number of efoldings increases rapidly with coupling

Oscillations of inflaton velocity are dampened

Gauge field helicity spectrum is smoothed and shifted

Abstract

We study the non-linear dynamics of axion inflation, capturing for the first time the inhomogeneity and full dynamical range during strong backreaction, till the end of inflation. Accounting for inhomogeneous effects leads to a number of new relevant results, compared to spatially homogeneous studies: i) the number of extra efoldings beyond slow roll inflation increases very rapidly with the coupling, ii) oscillations of the inflaton velocity are attenuated, iii) the tachyonic gauge field helicity spectrum is smoothed out (i.e.~the spectral oscillatory features disappear), broadened, and shifted to smaller scales, and iv) the non-tachyonic helicity is excited, reducing the chiral asymmetry, now scale dependent. Our results are expected to impact strongly on the phenomenology and observability of axion inflation, including gravitational wave generation and primordial black hole production.