TeV String Theories, Mini Black Holes and Trans-GZK Cosmic Rays

The existence of cosmic rays transcending the Greisen-Zatsepin-Kuzmin (GZK) cutoff appear to be a fact of life. While there is still some controversy regarding the observational data, it appears that opinions converge toward acknowledging the existence of trans-GZK events. Clearly, the issue will be satisfactorily clarified once future detectors, such as OWL, EUSO, the Pierre Auger Observatory, various neutrino telescopes, etc. will begin to take data. In the meantime, one may rely upon the existing set of observations and seek an understanding of the phenomenon. It is to be emphasized that if indeed trans-GZK cosmic ray events exist, they pose a serious challenge either to our current understanding of particle physics, or of astrophysics (or, perhaps, both).