New physics from ultrahigh energy cosmic rays

TL;DR

This paper discusses the implications of ultrahigh energy cosmic ray observations for new physics, focusing on the presence or absence of the GZK cutoff and its impact on understanding cosmic ray origins.

Contribution

It analyzes the contradictory experimental results regarding the GZK cutoff and explores the potential need for new physics if the cutoff is absent.

Findings

Contradictory results on the GZK cutoff existence

Implications for the origin of ultrahigh energy cosmic rays

Potential evidence for new physics beyond current models

Abstract

Observations of cosmic rays with energies above ~ 4 x 10^{10} GeV have inspired several speculative suggestions concerning their origin. The crucial question is whether or not the spectrum exhibits the expected `GZK cutoff' at this energy -- concerning which there are presently contradictory results. If there is indeed a cutoff, then the sources are cosmologically distant and rather exotic in nature. If there is no cutoff then new physics is required.