LIGHT GRAVITINOS AS MIXED DARK-MATTER

In theories with a gauge-mediated mechanism of supersymmetry breaking the gravitino is likely to be the lightest superparticle and, hence, a candidate for dark matter. We show that the decay of the next-to-ligh test superparticle into a gravitino can yield a non-thermal population of gravitinos which behave as a hot dark matter component. Together w ith the warm component, which is provided by the population of graviti nos of thermal origin, they can give rise to viable schemes of mixed d ark matter. This realization has some specific and testable features b oth in particle physics and astrophysics. We outline under which condi tions the mechanism remains viable even when R-parity is broken.