Global fits of axion-like particles to XENON1T and astrophysical data

The excess of electron recoil events seen by the XENON1T experiment has been interpreted as a potential signal of axion-like particles (ALPs), either produced in the Sun, or constituting part of the dark matter halo of the Milky Way. It has also been explained as a consequence of trace amounts of tritium in the experiment. We consider the evidence for the solar and dark-matter ALP hypotheses from the combination of XENON1T data and multiple astrophysical probes, including horizontal branch stars, red giants, and white dwarfs. We briefly address the influence of ALP decays and supernova cooling. While the different datasets are in clear tension for the case of solar ALPs, all measurements can be simultaneously accommodated for the case of a sub-dominant fraction of dark-matter ALPs. Nevertheless, this solution requires the tuning of several a priori unknown parameters, such that for our choices of priors a Bayesian analysis shows no strong preference for the ALP interpretation of the XENON1T excess over the background hypothesis.

Automated summary

The excess of electron recoil events observed in the XENON1T experiment has been proposed to potentially indicate axion-like particles (ALPs) originated from the Sun or dark matter halo, or due to trace amounts of tritium in the experiment. Combining XENON1T data with astrophysical probes supports the dark matter ALP hypothesis, despite the need for tuning unknown parameters. Bayesian analysis does not show strong preference for the ALP interpretation of the XENON1T excess over the background hypothesis, despite the tensions in the case of solar ALPs.