Antimatter signatures of gravitino dark matter decay

Abstract

The scenario of gravitino dark matter with brokenR-parity naturally reconciles three paradigms that, albeit very well motivatedseparately, seem to be in mutual conflict: supersymmetric dark matter, thermalleptogenesis and standard big bang nucleosynthesis. Interestingly, the products of thegravitino decay could be observed, opening the possibility of indirect detectionof gravitino dark matter. In this paper, we compute the positron and theantiproton fluxes from gravitino decay. We find that a gravitino with a mass ofm3/2∼150 GeV and alifetime of τ3/2∼1026 s could simultaneously explain the EGRET anomaly in the extragalactic diffuse gamma raybackground and the HEAT excess in the positron fraction. However, the predictedantiproton flux tends to be too large, although the prediction suffers from largeuncertainties and might be compatible with present observations for certain choices ofpropagation parameters.