Relic Neutrinos and [ITAL]Z[/ITAL]-Resonance Mechanism for Highest Energy Cosmic Rays

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Abstract
The origin of the highest energy cosmic rays remains elusive. The decay of a superheavy particle (X) into an ultraenergetic neutrino which scatters from a relic neutrino or antineutrino at the Z-resonance has attractive features. Given the necessary X mass of 1014-1015 GeV, the required lifetime, 1015-1016 yr, renders model building a serious challenge, but three logical possibilities are considered: (1) X is a Higgs scalar in SU(15) belonging to high-rank representation, leading to power-enhanced lifetime; (2) a global X quantum number has exponentially suppressed symmetry breaking by instantons; and (3) with additional space dimension(s), localization of X within the real-world brane leads to Gaussian decay suppression, the most efficient of the suppression mechanisms considered.