Cosmic-ray positrons from annihilation of weakly interacting massive particles in the galaxy

The production of cosmic-ray positrons from the annihilation of weakly interacting massive particles (WIMP's) is considered. Conventional supersymmetric-neutralino annihilation generally yields an unobservably small e^+ flux. However, a massive WIMP (20 GeV) with a large annihilation cross section into a single e^+e^- pair produces a distinctive and observable shelf in the cosmic-ray e^+ spectrum. Only Dirac neutrinos obviously generate such a feature, but it may also appear in more elaborate neutralino models. Such models are constrained by upper limits on the low-energy antiproton flux.