Cosmic rays of ultrahigh energy

A new phenomenon-giant air showers of energy above 10(20) eV, which lie beyond the Greisen-Zatsepin-Kuzmin cutoff-was discovered by various detection methods. The mechanism of particle acceleration to such high energies is still a puzzle. The arrival directions of giant showers do not contradict the hypothesis of their isotropic distribution. There are indications of their correlations with distant objects. It is obvious that only observations at new arrays can clarify the problem. The observed events must be reanalyzed within a more elaborate scheme. Verification of slight deviations from Lorentz invariance is possible. (c) 2005 Pleiades Publishing, Inc.