Probing photophobic (rel)axion dark matter

TL;DR

This paper explores a relaxion dark matter model where a keV-mass relaxion with suppressed photon couplings can explain the XENON1T excess and satisfy cosmological and astrophysical constraints.

Contribution

It introduces a relaxion dark matter scenario with naturally suppressed photon couplings, linking early universe cosmology to direct detection signals.

Findings

A 3 keV relaxion can account for dark matter and the XENON1T excess.

The model satisfies astrophysical and cosmological constraints.

The relaxion-electron coupling is consistent with experimental bounds.

Abstract

We investigate the interplay between early universe cosmology and dark matter direct detection, considering axion models with naturally suppressed couplings to photons. In the context of the cosmological relaxation of the electroweak scale, we focus on a scenario of \emph{Relaxion Dark Matter}, in which the relaxion field constitutes all the observed dark matter relic density and its allowed mass range is fixed to a few $\mathrm{keV}$ by construction. In particular, we show that a relaxion particle with mass $m_\phi= 3.0 \,\mathrm{keV}$ which couples to electrons with $g_{\phi, e}= 6.8 \times 10^{-14}$ is consistent with the XENON1T excess, while accounting for the observed dark matter and satisfying astro/cosmo probes. This scenario uses the electroweak scale as the link connecting the relaxion production at early times with the dark matter absorption rate in direct detection.