Testing Thermal-Relic Dark Matter with a Dark Photon Mediator

TL;DR

This paper evaluates the viability of thermal-relic dark matter models mediated by dark photons, using recent experimental results to exclude or support different parameter regimes, and highlights future experimental prospects.

Contribution

It provides the first comprehensive analysis of dark photon mediated dark matter in light of recent DAMIC-M results, identifying excluded and viable parameter spaces for various models.

Findings

Direct-annihilation regime for complex scalar dark matter is mostly excluded.

Resonant annihilation remains viable for specific mass relations.

Secluded annihilation is excluded for dark matter masses below 30 GeV.

Abstract

In light of recent DAMIC-M results, we present the status of thermal-relic dark matter $\chi$ coupled to a kinetically-mixed dark photon $A^\prime$. In the predictive "direct annihilation" regime, $m_{A'} > m_\chi$, the relic abundance depends on the kinetic mixing parameter, and there is a minimum value compatible with thermal freeze out. Using only electron and nuclear recoil direct detection results, we find that for complex scalar dark matter, the direct-annihilation regime is now excluded for nearly all values of $m_\chi$; the only exception is the resonant annihilation regime where $m_{A'}\approx 2 m_\chi$. Direct annihilation relic targets for other representative models, including Majorana and Pseudo-Dirac candidates, remain viable across a wide range of model parameters, but will be tested with a combination of dedicated accelerator searches in the near future. In the opposite "secluded annihilation" regime, where $m_\chi > m_{A'}$, this scenario is excluded by cosmic microwave background measurements for all $m_\chi \lesssim 30$ GeV. Similar conclusions in both the direct and secluded regimes hold for all anomaly-free vector mediators that couple to the first generation of electrically-charged Standard Model particles.