Abstract
We suggest a new signature for particle dark-matter annihilation in the halo: high-energy, positron line radiation. Because the cosmic-ray positron spectrum falls rapidly with energy and the contribution of conventional sources is only expected to be about 5% of the cosmic-ray electron flux, monoenergetic ’s from halo annihilations can be a significant and distinctive signal for very massive dark-matter particles (masses greater than about 30 GeV). If the annihilation channel has an appreciable branch—a few percent or more—the signal could be observable in a future detector, such as have been proposed for ASTROMAG. A significant branching ratio can occur for neutralinos or Dirac neutrinos. In spite of the fact that a heavy Dirac neutrino is no longer an attractive dark-matter candidate and the fact that the branching ratios expected for the currently popular models of the neutralino are very small, the positron signature is so distinctive that we believe it is worthy of note: If seen, it is a ‘‘smoking gun’’ for particle dark matter in the halo. We also note that the positron signature will be of general importance for any future particle dark-matter candidate whose annihilation into is not suppressed.
- Received 21 February 1990
DOI:https://doi.org/10.1103/PhysRevD.42.1001
©1990 American Physical Society