We revisit the possibility of light-scalar dark matter, in the MeV to GeV mass bracket and coupled to electrons through fermion or vector mediators, in light of significant experimental and observational advances that probe new physics below the GeV scale. We establish new limits from electron colliders and fixed-target beams and derive the strength of loop-induced processes that are probed by precision physics, among other laboratory probes. In addition, we compute the cooling bound from SN1987A, consider self-scattering, structure formation, and cosmological constraints as well as the limits from dark matter–electron scattering in direct detection experiments. We then show that the combination of constraints largely excludes the possibility that the galactic annihilation of these particles may explain the long-standing International Gamma-Ray Astrophysics Laboratory excess of 511 keV photons as observed in the Galactic bulge. As a caveat to these conclusions, we identify the resonant annihilation regime where the vector mediator goes nearly on shell.

• Received 2 November 2020
• Accepted 28 February 2021

DOI:https://doi.org/10.1103/PhysRevD.103.075005

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