Ultra high energy cosmic rays

Abstract

The current status of Ultra High Energy Cosmic Rays (UHECR) is reviewed, with emphasis given to elementary particle solutions to UHECR problem, namely to Topological Defects and Super-Heavy Dark Matter Particles (SHDMP). The relic superheavy particles are very efficiently produced at inflation. Being protected by gauge discrete symmetries, they can be long lived. They are clustering in the Galactic halo, producing thus UHECR without Greisen-Zatsepin-Kuzmin cutoff. Topological Defects can naturally produce particles with energies as observed and much higher, but in most cases fail to produce the observed fluxes. Cosmic necklaces, monopoles connected by strings and vortons are identified as most plausible sources. The latter two of them are also clustering in the halo and their observational predictions are identical to those of SHDMP.