Disappointing model for ultrahigh-energy cosmic rays

TL;DR

This paper proposes a model for ultrahigh-energy cosmic rays that suggests limited acceleration energies and predicts no cosmogenic neutrinos, GZK cutoff, or source correlation, challenging existing expectations.

Contribution

The paper introduces a model assuming low maximum acceleration energies for extragalactic protons and rigidity-dependent acceleration for heavier nuclei, leading to specific observational consequences.

Findings

No pion photo-production on CMB photons in this model

Absence of high-energy cosmogenic neutrino fluxes

No GZK cutoff or source correlation at highest energies

Abstract

Data of Pierre Auger Observatory show a proton-dominated chemical composition of ultrahigh-energy cosmic rays spectrum at (1 - 3) EeV and a steadily heavier composition with energy increasing. In order to explain this feature we assume that (1 - 3) EeV protons are extragalactic and derive their maximum acceleration energy, E_p^{max} \simeq 4 EeV, compatible with both the spectrum and the composition. We also assume the rigidity-dependent acceleration mechanism of heavier nuclei, E_A^{max} = Z x E_p^{max}. The proposed model has rather disappointing consequences: i) no pion photo-production on CMB photons in extragalactic space and hence ii) no high-energy cosmogenic neutrino fluxes; iii) no GZK-cutoff in the spectrum; iv) no correlation with nearby sources due to nuclei deflection in the galactic magnetic fields up to highest energies.