Comment on the "Second dip as a signature of ultrahigh energy proton interactions with cosmic microwave background radiation" by V.Berezinsky, A.Gazizov and K.Kachelriess

Abstract

A new feature in the spectrum of ultra high energy cosmic rays (UHECR) has been announced in the paper by Berezinsky, Gazizov and Kachelriess. The ratio of the solution of the exact transport equation to its solution in the continuous energy loss limit shows intriguing features which, according to the Authors, are related to the very nature of the energy loss processes of UHECR:the very sharp second dip predicted at 6.3x10^19 eV can be used as an energy calibration point and also as the UHECR mass indicator for big future cosmic ray experiments. In the present paper we would like to advocate that this statement is an overinterpretation. The second dip is a result of an inapproriate approximation used, and thus it can't help to understand the nature of UHECR in any way.