Natural candidates for superheavy dark matter in string and M theory

Abstract

We reconsider superheavy dark matter candidates in string and M theory, in view of the possibility that inflation might generate superheavy particles with an abundance close to that required for a near-critical Universe. We argue that cryptons---stable or metastable bound states of matter in the hidden sector---are favored over other possible candidates in string or M theory, such as the Kaluza-Klein states associated with extra dimensions. We exhibit a specific string model that predicts cryptons as hidden-sector bound states weighing $\ensuremath{\sim}{10}^{12} \mathrm{GeV},$ and discuss their astrophysical observability.