Ultra-high-energy cosmic rays from collisional annihilation revisited

Abstract

We re-examine collisional annihilation of super-heavy dark-matter particles in dark-matter density spikes in the galactic halo as a possible source of ultra-high-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 super-heavy dark matter if the particles can form dense cores in the 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.PACS Nos.: 98.70.Sa, 98.70.–f, 95.35.+d, 14.80.–j