Re-examining the Solar Axion Explanation for the XENON1T Excess

TL;DR

This paper re-evaluates the solar axion explanation for the XENON1T excess, highlighting the importance of the inverse Primakoff process and exploring new physics scenarios to reconcile with astrophysical constraints.

Contribution

It demonstrates that including the inverse Primakoff process reduces tension with astrophysical bounds and investigates new physics to further resolve discrepancies.

Findings

Inverse Primakoff process significantly impacts detection signals.

Including this process reduces tension with astrophysical constraints.

Exploration of new physics scenarios further alleviates bounds.

Abstract

The XENON1T collaboration has observed an excess in electronic recoil events below $5~\mathrm{keV}$ over the known background, which could originate from beyond-the-Standard-Model physics. The solar axion is a well-motivated model that has been proposed to explain the excess, though it has tension with astrophysical observations. The axions traveled from the Sun can be absorbed by the electrons in the xenon atoms via the axion-electron coupling. Meanwhile, they can also scatter with the atoms through the inverse Primakoff process via the axion-photon coupling, which emits a photon and mimics the electronic recoil signals. We found that the latter process cannot be neglected. After including the $\rm{keV}$ photon produced via inverse Primakoff in the detection, the tension with the astrophysical constraints can be significantly reduced. We also explore scenarios involving additional new physics to further alleviate the tension with the astrophysical bounds.