Ultra-high energy cosmic rays from annihilation of superheavy dark matter

We consider the possibility that ultra-high energy cosmic rays originate from the annihilation of relic superheavy darkmatter.We find that a cross section of 〈σAv〉 ∼ 10cm(MX/10 GeV)3/2 is required to account for the observed rate of super-GZK events if the superheavy dark matter follows a Navarro–Frenk–White density profile. This would require extremely large-l contributions to the annihilation cross section. We also calculate the possible signature from annihilation in sub-galactic clumps of dark matter and find that the signal from sub-clumps dominates and may explain the observed flux with a much smaller cross section than if the superheavy dark matter is smoothly distributed. Finally, we discuss the expected anisotropy in the arrival directions of the cosmic rays, which is a characteristic signature of this scenario.