Probing the Cosmic Axion Background via Axion-Photon Conversion in Filaments

Duncan Rocha; Gordan Krnjaic; Matthew J. Baldwin

Probing the Cosmic Axion Background via Axion-Photon Conversion in Filaments

High Energy Physics - Phenomenology 2026-07-20 v1

Authors: Duncan Rocha , Gordan Krnjaic , Matthew J. Baldwin

Abstract

The cosmic axion background (CaB) is a hypothetical population of relativistic axions produced in the early universe. If the CaB is produced from dark matter decays, the axions in this population can convert to photons in the magnetic fields of cosmological filaments, resulting in an isotropic gamma ray background flux. We present new indirect detection constraints on the axion mass and axion-photon coupling, for GeV-TeV dark matter with a decay lifetime below $10^{30}$ sec, by comparing this flux against experimental data. We exclude significant parameter space for axion masses below $10^{-5}$ ~eV for a broad range of dark matter masses and lifetimes, assuming conservative filament magnetic field strengths ( $\sim 1$ nG). For large filament fields ( $\sim 100$ nG), our strategy also constrains a portion of the QCD-axion parameter space for TeV-scale dark matter masses.

Keywords

cosmic axion background axion-photon conversion dark matter decay gamma-ray background filament magnetic fields indirect detection

Cite

@article{arxiv.2607.18372,
  title  = {Probing the Cosmic Axion Background via Axion-Photon Conversion in Filaments},
  author = {Duncan Rocha and Gordan Krnjaic and Matthew J. Baldwin},
  journal= {arXiv preprint arXiv:2607.18372},
  year   = {2026}
}