ar X iv : a st ro - p h / 05 01 13 3 v 2 2 7 M ay 2 00 5 1 Ultrahigh energy cosmic rays from collisional annihilation revisited

We re-examine collisional annihilation of superheavy dark matter particles in dark matter density spikes in the galactic halo as a possible source of ultrahigh energy cosmic rays. We estimate the possible flux in a way that does not depend on detailed assumptions about the density profiles of dark matter clumps. The result confirms that collisional annihilation is compatible with annihilation cross sections below the unitarity bounds for superheavy dark matter if the particles can form dense cores in dark matter substructure, and it provides estimates for core sizes and densities. The ensuing clumpy source distribution in the galactic halo will be tested within a few years of operation of the Pierre Auger observatory.