Terrestrial Probes of Electromagnetically Interacting Dark Radiation

TL;DR

This paper investigates how dark radiation from dark matter decay could interact electromagnetically, producing detectable signals in experiments and potentially explaining the XENON1T excess.

Contribution

It introduces the idea that dark radiation with electromagnetic interactions can be detected and explains the XENON1T anomaly, providing new sensitivity estimates for such interactions.

Findings

Direct detection experiments can probe electromagnetic couplings down to ~10^{-11}

Dark radiation can account for the XENON1T electron recoil excess

Complementary sensitivity between direct detection and neutrino experiments

Abstract

We study the possibility that dark radiation, sourced through the decay of dark matter in the late Universe, carries electromagnetic interactions. The relativistic flux of particles induces recoil signals in direct detection and neutrino experiments through its interaction with millicharge, electric/magnetic dipole moments, or anapole moment/charge radius. Taking the DM lifetime as 35 times the age of the Universe, as currently cosmologically allowed, we show that direct detection (neutrino) experiments have complementary sensitivity down to $\epsilon\sim 10^{-11}$ $(10^{-12})$, $d_\chi/\mu_\chi \sim 10^{-9}\,\mu_B$ $(10^{-13}\mu_B)$, and $a_\chi/b_\chi \sim 10^{-2}\,{\rm GeV}^{-2}$ $(10^{-8}\,{\rm GeV}^{-2})$ on the respective couplings. Finally, we show that such dark radiation can lead to a satisfactory explanation of the recently observed XENON1T excess in the electron recoil signal without being in conflict with other bounds.