With excellent energy resolution and ultralow-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 ($\chi +\chi +A\to \varphi +A$), 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 ${}^{76}\mathrm{Ge}$-enriched detectors whose surface exposure time was carefully controlled, resulting in extremely low levels of cosmogenic activation.

• Received 23 June 2022
• Revised 8 September 2023
• Accepted 9 November 2023

DOI:https://doi.org/10.1103/PhysRevLett.132.041001

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society