Secondary protons from ultra high energy cosmic ray nuclei: is the Greisen-Zatsepin-Kuzmin cutoff unavoidable?

TL;DR

This paper investigates the production of secondary protons from ultra high energy cosmic ray nuclei and finds that the GZK cutoff is unavoidable due to secondary proton dominance at high energies.

Contribution

It introduces a model assuming fixed atomic mass nuclei as primaries and calculates the resulting secondary proton spectrum, confirming the inevitability of the GZK cutoff.

Findings

Secondary protons dominate over primary nuclei at energies around 1-2 x 10^19 eV.

The GZK cutoff naturally arises from secondary proton production.

The spectrum calculation supports the standard GZK suppression in cosmic rays.

Abstract

We discuss the production of ultra high energy secondary protons by cosmic ray primary nuclei propagating in the intergalactic space through Cosmic Microwave Background (CMB) and Infrared (IR) radiations. Under the assumption that only primary nuclei with a fixed atomic mass number $A_0$ are accelerated, the spectrum of secondary protons is calculated. It is found that for all $A_0$ the diffuse flux of secondary protons starts to dominate over that of primary nuclei at energy $E \sim (1 - 2)\times 10^{19}$ eV, and thus the standard Greisen-Zatsepin -Kuzmin (GZK) cutoff is produced.