Non-extensivity effects and the highest energy cosmic ray affair

Recent measurements of the cosmic microwave background confirm that it is d escribed by a Planckian distribution with high precision. It is non-extensi vity bounded to be less than some parts in 10(5), or to some parts in 10(4) at most. This deviation may appear minuscule, but may have a non-negligibl e effect on a particle propagating through this background over the course of millions of years. In this Letter we analyze the possible influence of s uch a slight deviation upon the propagation of nuclei and protons of ultra- high energy. These particles interact via photopion and photodisintegration processes which we examine taking into account a slight non-extensive back ground. We show that such a deviation does not exhibit a significant differ ence in the energy attenuation length of extremely high energy cosmic rays. (C) 2001 Elsevier Science B.V. All rights reserved.