MeV Dark Matter Complementarity and the Dark Photon Portal

TL;DR

This paper explores the phenomenology of MeV-scale Dirac fermion dark matter interacting via a dark photon, analyzing relic density, detection prospects, and constraints from cosmology and future gamma-ray telescopes.

Contribution

It provides a comprehensive analysis of MeV dark matter with a dark photon portal, including relic density calculations and the impact of cosmological and experimental constraints.

Findings

Stringent CMB constraints limit thermal production of MeV dark matter.

e-ASTROGAM can potentially detect dark matter below 10 MeV.

Late-time inflation and freeze-in mechanisms can produce the correct relic density.

Abstract

We discuss the phenomenology of an MeV-scale Dirac fermion coupled to the Standard Model through a dark photon with kinetic mixing with the electromagnetic field. We compute the dark matter relic density and explore the interplay of direct detection and accelerator searches for dark photons. We show that precise measurements of the temperature and polarization power spectra of the Cosmic Microwave Background Radiation lead to stringent constraints, leaving a small window for the thermal production of this MeV dark matter candidate. The forthcoming MeV gamma-ray telescope e-ASTROGAM will offer important and complementary opportunities to discover dark matter particles with masses below 10 MeV. Lastly, we discuss how a late-time inflation episode and freeze-in production could conspire to yield the correct relic density while being consistent with existing and future constraints.