Axion Inflation with a Massive Abelian Gauge Field
Abstract
An axial coupling between an inflaton and an Abelian gauge field can trigger the tachyonic amplification of one gauge-field helicity. For a massless vector, modes with physical momentum k/a∼ |ξ|H are enhanced by approximately exp(π|ξ|), and sufficiently efficient production can provide substantial friction for the homogeneous inflaton. We extend this mechanism to a vector of mass m. The instability is present only for |ξ|>m̅≡ m/H, and in the heavy regime the mode amplitude scales as exp[π(|ξ|−m̅)]. Because the amplified modes remain well inside the Hubble radius when m̅≫1, their contribution to long-wavelength curvature perturbations ζ is power-law suppressed at fixed background backreaction. In the weak-backreaction regime we obtain a spectrum cal Pidζ ∝ m̅−w, with w ∼ 2, while including the gauge-induced friction of scalar perturbations gives the scaling cal Pidζ∝ m̅−s, with s between three and four. These estimates indicate that cal Pidζ≲ 10−9 on CMB scales should be compatible with gauge field backreaction for m̅ larger than order a few hundred. We test the analytical mode functions and backreaction estimates with the first lattice simulations based on a massive-vector extension of the \texttt{Pencil Code}, including simulations in the strongly backreacting regime.
Related
BibTeX
@misc{ferreira2026axion,
title = {{Axion Inflation with a Massive Abelian Gauge Field}},
author = {Ricardo Z. Ferreira and Alessio Notari and José Jaime Terente Díaz},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.28593},
eprint = {2607.28593},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.28593},
}
RIS
TY - UNPB
TI - Axion Inflation with a Massive Abelian Gauge Field
AU - Ricardo Z. Ferreira
AU - Alessio Notari
AU - José Jaime Terente Díaz
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2607.28593
UR - https://arxiv.org/abs/2607.28593
AB - An axial coupling between an inflaton and an Abelian gauge field can trigger the tachyonic amplification of one gauge-field helicity. For a massless vector, modes with physical momentum k/a∼ |ξ|H are enhanced by approximately exp(π|ξ|), and sufficiently efficient production can provide substantial friction for the homogeneous inflaton. We extend this mechanism to a vector of mass m. The instability is present only for |ξ|>m̅≡ m/H, and in the heavy regime the mode amplitude scales as exp[π(|ξ|−m̅)]. Because the amplified modes remain well inside the Hubble radius when m̅≫1, their contribution to long-wavelength curvature perturbations ζ is power-law suppressed at fixed background backreaction. In the weak-backreaction regime we obtain a spectrum cal P^id_ζ ∝ m̅^−w, with w ∼ 2, while including the gauge-induced friction of scalar perturbations gives the scaling cal P^id_ζ∝ m̅^−s, with s between three and four. These estimates indicate that cal P^id_ζ≲ 10^−9 on CMB scales should be compatible with gauge field backreaction for m̅ larger than order a few hundred. We test the analytical mode functions and backreaction estimates with the first lattice simulations based on a massive-vector extension of the \texttt{Pencil Code}, including simulations in the strongly backreacting regime.
ER -