Extremely high energy cosmic rays from relic particle decays

The expected proton and neutrino fluxes from decays of massive metastable r elic particles are calculated using the HERWIG QCD event generator. The pre dicted proton spectrum can account for the observed flux of extremely high energy cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff, for a decayin g particle mass of O(10(12)) GeV. The lifetime required is of O(10(20)) yr if such particles constitute all of the dark matter (with a proportionally shorter lifetime for a smaller contribution). Such values are plausible if the metastable particles are hadron-like bound states from the hidden secto r of supersymmetry breaking which decay through nonrenormalizable interacti ons. The expected ratio of the proton to neutrino flux is given as a diagon istic of the decaying particle model for the forthcoming Pierre Auger Proje ct. (C) 1998 Elsevier Science B.V.