Axion-Photon Conversion and Effects on 21cm Observation

TL;DR

This paper explores how axion-like particles converting into photons in intergalactic magnetic fields could explain the anomalous 21cm absorption signal observed by EDGES, suggesting a novel heating mechanism for the cosmic microwave background.

Contribution

It proposes a new mechanism where axion-photon conversion in magnetic fields can account for the EDGES 21cm signal anomaly, linking particle physics with cosmological observations.

Findings

Axion-like particles can resonantly convert into photons in intergalactic magnetic fields.

This conversion can significantly heat the cosmic microwave background in relevant frequency ranges.

The proposed mechanism offers a potential explanation for the EDGES 21cm absorption anomaly.

Abstract

Recently the EDGES experiment reported an enhanced 21cm absorption signal in the radio wave observation, which may be interpreted as either anomalous cooling of baryons or heating of cosmic microwave background photons. In this paper, we pursue the latter possibility. We point out that dark radiation consisting of axion-like particles can resonantly convert into photons under the intergalactic magnetic field, which can effectively heat up the radiation in the frequency range relevant for the EDGES experiment. This may explain the EDGES anomaly.