Sub-keV dark matter can strongly ionize molecular clouds
Phys. Rev. D 113, 063035 – Published 20 March, 2026
DOI: https://doi.org/10.1103/qmw9-1k4k
Abstract
The ionization of dense molecular clouds offers a powerful and robust probe of dark matter models that produce UV or x-ray photons via annihilation or decay. Using this novel observable, we derive competitive constraints on dark matter in the mass range from 30 eV to 1 keV. In particular, we set the strongest existing limits on axionlike dark matter in the 30–100 eV range. We also present sensitivity projections demonstrating the significant potential of this approach. These constraints can be substantially improved with targeted observations of molecular clouds near the Galactic Center and above the Galactic plane as well as with a more accurate modeling of cosmic-ray ionization and refined gas density estimates from dust extinction maps. Our results establish molecular cloud ionization as one of the most sensitive tools for probing sub-keV dark matter.
