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

TL;DR

This paper evaluates axion-like particles as an explanation for the XENON1T electron recoil excess, analyzing astrophysical and experimental data, and finds that a dark matter ALP scenario is plausible but not strongly preferred.

Contribution

It provides a comprehensive combined analysis of XENON1T and astrophysical data to test ALP hypotheses, highlighting the challenges in confirming ALPs as the cause of the excess.

Findings

Dark-matter ALPs can fit the data with parameter tuning.

Solar ALPs are in tension with astrophysical constraints.

Bayesian analysis shows no strong preference for ALPs over background.

Abstract

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.