Retuning radio astronomy for axion dark matter with neutron stars

TL;DR

This paper models axion-to-photon conversion in neutron star magnetospheres, suggesting detectable high-frequency radio signals that could reveal axion dark matter up to about a millielectronvolt, especially in sources like SGR 1745--2900.

Contribution

It introduces a new model accounting for charge acceleration effects, expanding the predicted frequency range and potential detectability of axion-induced signals in neutron star environments.

Findings

Heavier axions can resonate in magnetospheric splits, producing detectable signals.

The frequency range for axion detection extends into the millimeter band.

Neutron stars like SGR 1745--2900 are promising targets for high-frequency axion searches.

Abstract

A model is constructed to predict the emission originating from axion-to-photon conversion in the strongly magnetized ultrarelativistic plasma of neutron stars. The acceleration and multiplicity of the charges are observed to shift the axion-induced spectral feature with respect to previous expectations. The frequency range of interest widens accordingly, and heavier dark matter axions may resonate in magnetospheric splits giving rise to detectable radio signals that could extend into the millimeter band. Ultimately, this work follows an affirmative answer to the question of whether neutron stars can give rise to any detectable high-frequency spectral feature that would allow us to probe axion dark matter of masses up to about a millielectronvolt. SGR 1745--2900 emerges as a particularly promising astrophysical laboratory for probing high-frequency axion dark matter.