Constraining resonant photon-axion conversions in the Early Universe

TL;DR

This paper uses precise CMB spectral data to set new bounds on photon-axion-like particle conversions in the early Universe, constraining the coupling strength and magnetic field interactions.

Contribution

It derives the first bounds on resonant photon-ALP conversions during the Universe's thermal history using FIRAS data, improving constraints on ALP properties.

Findings

Upper limits on g B > 10^{-13} GeV^{-1} nG for ALP masses below eV

Constraints improve previous bounds on photon-ALP interactions

Results inform models of primordial magnetic fields and ALP physics

Abstract

The presence of a primordial magnetic field would have induced resonant conversions between photons and axion-like particles (ALPs) during the thermal history of the Universe. These conversions would have distorted the blackbody spectrum of the cosmic microwave background (CMB). In this context, we derive bounds on the photon-ALP resonant conversions using the high precision CMB spectral data collected by the FIRAS instrument on board of the Cosmic Background Explorer. We obtain upper limits on the product of the photon-ALP coupling constant g times the magnetic field strength B down to g B > 10^{-13} GeV^{-1} nG for ALP masses below the eV scale.