Search for Dark Matter Annihilation and Decay with H$\alpha$ Line Emission

TL;DR

This paper proposes a novel indirect method to detect dark matter by observing H-alpha emission resulting from ionization caused by dark matter annihilation or decay, providing new constraints in the eV-GeV mass range.

Contribution

It introduces the first H-alpha based limits on dark matter annihilation and decay, demonstrating the potential of H-alpha imaging as a new dark matter search technique.

Findings

Non-detection of extended H-alpha emission in Leo T sets new limits on dark matter properties.

H-alpha emission can effectively trace dark matter energy injection in gas-rich dwarf galaxies.

Upcoming telescopes can improve sensitivity, expanding the search for dark matter signals.

Abstract

I present a new indirect search for dark matter (DM) using Hydrogen-$\alpha$ (H$\alpha$) recombination emission. DM annihilation or decay products can ionize neutral gas; subsequent recombination cascades generate H$\alpha$ photons through the $3\rightarrow2$ transition. In quiet gas-rich dwarf galaxies, the $n{=}2$ population is negligible, so H$\alpha$ is effectively unabsorbed and traces the DM-energy injection site. Using the non-detection of extended H$\alpha$ emission in the Leo T dwarf galaxy with Multi Unit Spectroscopic Explorer (MUSE) observations, I derive the first H$\alpha$-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 H$\alpha$ imaging as a powerful DM search strategy.