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 dark matter. We find that across-section of <sigma(A)v> similar to 10(-2)6 cm(2) (M-X/10(12) 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. (C) 2002 Elsevier Science B.V. All rights reserved.