Ultra high-energy cosmic ray proton interactions

The recent Auger results suggest that the coincidences of arrival directions with ‘nearby’ AGN, and the HiRes discovery of the GZK cut-off, indicate protons to be at least the strongly dominant component of primary extra galactic cosmic ray flux. The measured longitudinal extensive air shower propagation characteristics, however, indicate at least a mixed composition, if the conventional interaction model is correct. For the present work we assume that the particles are indeed protons and examine the consequences for the high-energy interaction physics. We have found that such a supposition requires strong violation of the so-called Feynman scaling.