The energy spectra of ultra high energy cosmic rays reported by the AGASA, Fly’s Eye, Haverah Park, HiRes, and Yakutsk experiments are all shown to be in agreement with each other for energies below 10 eV (after small adjustments, within the known uncertainties, of the absolute energy scales). The data from HiRes, Fly’s Eye, and Yakutsk are consistent with the expected flux suppression above 5 ...

Data from the High Resolution Fly’s Eye detector that measures cosmic rays with the fluorescence technique is used to set limits on the flux of tau neutrinos in the energy range from 10 to 10 eV. This energy range is particularly interesting as we expect a guaranteed flux of cosmogenic neutrinos from the GZK mechanism.

Two processes of matter creation after inflation: 1) gravitational creation of superheavy (quasi)stable particles, and 2) non-thermal phase transitions leading to formation of topological defects, may be relevant to the resolution of the puzzle of cosmic rays observed with energies beyond GZK cut-off. Both possibilities are reviewed in this talk.