Ultrahigh Energy Cosmic Rays without Greisen-Zatsepin-Kuzmin Cutoff

Abstract

We study the decays of metastable superheavy particles as the source of ultrahigh energy cosmic rays (UHE CR). These particles are assumed to constitute a tiny fraction ${\ensuremath{\xi}}_{X}$ of cold dark matter in the Universe. The UHE CR fluxes produced at the decays of $X$ particles are calculated. The dominant contribution is given by fluxes of photons and nucleons from the halo of our Galaxy and thus does not exhibit the GZK cutoff. The extragalactic components of UHE CR are suppressed by the smaller extragalactic density of $X$ particles and, hence, the cascade limit is relaxed. We discuss the spectrum of produced extensive air showers and a signal from a Virgo cluster as signatures of this model.