Ultra high energy cosmic rays

Abstract

The current status of Ultra High Energy Cosmic Rays (UHECR) is reviewed, with\nemphasis given to theoretical interpretation of the observed events. The\ngalactic and extragalactic origin, in case of astrophysical sources of UHE\nparticles, have the problems either with acceleration to the observed energies\nor with the fluxes and spectra. Topological defects can naturally produce\nparticles with energies as observed and much higher, but in most cases fail to\nproduce the observed fluxes. Cosmic necklaces and monopole-antimonopole pairs\nare identified as most plausible sources, which can provide the observed flux\nand spectrum. The relic superheavy particles are shown to be clustering in the\nGalactic halo, producing UHECR without Greisen-Zatsepin-Kuzmin cutoff. The\nLightest Supersymmetric Particles are discussed as UHE carriers in the\nUniverse.\n