Probing the structure of space-time with cosmic rays

The study of the interactions of cosmic rays (CR's) with universal diffuse background radiation can provide very stringent rests of the validity of special relativity. The interactions we consider are the ones characterized by well defined energy thresholds whose energy position can be predicted on the basis of special relativity. We argue that the experimental confirmation of the existence of these thresholds can in principle put very stringent limits on the scale where special relativity and/or continuity of space-time may possibly break down.