Exotic dark matter search with the Majorana Demonstrator

With excellent energy resolution and ultra-low level radiogenic backgrounds, the high-purity germanium detectors in the Majorana Demonstrator enable searches for several classes of exotic dark matter (DM) models. In this work, we report new experimental limits on keV-scale sterile neutrino DM via the transition magnetic moment from conversion to active neutrinos, ${\nu }_s\to {\nu }_a$. We report new limits on fermionic dark matter absorption ($\chi +A\to \nu +A$) and sub-GeV DM-nucleus 3$\to$2 scattering ($\chi +\chi +A\to \phi +A$), and new exclusion limits for bosonic dark matter (axionlike particles and dark photons). These searches utilize the (1–100)-keV low energy region of a 37.5-kg y exposure collected by the Demonstrator between May 2016 and November 2019, using a set of ${}^{76}$Ge-enriched detectors whose surface exposure time was carefully controlled, resulting in extremely low levels of cosmogenic activation.