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 {ital e}{sup +} flux. However, a massive WIMP ({approx gt}20 GeV) with a large annihilation cross section into a single {ital e}{sup +}e{sup {minus}} pair produces a distinctive and observable shelf in the cosmic-ray {ital e}{sup +} 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.