Electromagnetic signals of inelastic dark matter scattering

A bstract Light dark sectors in thermal contact with the Standard Model can naturally produce observed relic matter abundance and are targets of a broad experimental search program. key light sector model is pseudo-Dirac fermion photon mediator. The dynamics fermionic excited states often neglected. We consider scenarios which nontrivial produced their subsequent de-excitation yields interesting electromagnetic signals direct detection experiments. study three mechanisms populating state: primordial fraction, component up-scattered Sun, Earth. find that fractional generically depleted to exponentially small fractions early universe. Nonetheless, this observable current searches. MeV-scale cross sections higher be probed by down-scattering following excitation Sun. Up-scatters GeV-scale Earth give rise upcoming terrestrial experiments X-ray observations. comment on possible relevance these recent excess XENON1T.