Cosmological neutrino signatures for grand unification scale physics

Physics beyond the standard model might imply the cosmological production of particles with grand unification scale energies. Nucleons and γ-rays from such processes are candidates for the cosmic rays observed beyond 100 EeV (1020 eV). Using a new particle propagation code, we calculate the neutrino fluxes predicted by such scenarios if consistency with the observed cosmic ray flux and the universal γ-ray background at 1–10 GeV is required. Flux levels detectable by proposed km3 scale neutrino observatories are allowed by these constraints. Bounds on or detection of a neutrino flux above ∼ 1 EeV would allow neutrino astronomy to probe grand unification scale physics.