Search for Dark Matter Annihilation and Decay with Hα Line Emission.

I present a new indirect search for dark matter (DM) using hydrogen-α (Hα) recombination emission. DM annihilation or decay products can ionize neutral gas; subsequent recombination cascades generate Hα photons through the 3→2 transition. In quiet gas-rich dwarf galaxies, the n=2 population is negligible, so Hα is effectively unabsorbed and traces the DM-energy injection site. Using the nondetection of extended Hα emission in the Leo T dwarf galaxy with Multi Unit Spectroscopic Explorer observations, I derive the first Hα-based limits on DM annihilation and decay, reaching leading sensitivity for parts of the eV-GeV mass range. Existing and upcoming telescopes can further extend this reach, establishing Hα imaging as a powerful DM search strategy.