PLASMA EFFECTS ON EXTRAGALACTIC ULTRA-HIGH-ENERGY COSMIC RAY HADRON BEAMS IN COSMIC VOIDS

The linear instability of an ultrarelativistic hadron beam (Gamma(b) approximate to 10(6)) in the unmagnetized intergalactic medium (IGM) is investigated with respect to the excitation of collective electrostatic and aperiodic electromagnetic fluctuations. This analysis is important for the propagation of extragalactic ultrarelativistic cosmic rays (E > 10(15) eV) from their distant sources to Earth. We calculate minimum instability growth times that are orders of magnitude shorter than the cosmic ray propagation time in the IGM. Due to nonlinear effects, especially the modulation instability, the cosmic ray beam stabilizes and can propagate with nearly no energy loss through the IGM.