Testing fundamental principles with high-energy cosmic rays

TL;DR

This paper explores whether ultra-high energy cosmic ray flux suppression indicates the GZK cutoff or source energy limits, examining potential violations of fundamental physics principles like Lorentz symmetry and their implications for high-energy astrophysics.

Contribution

It provides an updated analysis of how Lorentz symmetry violations could influence cosmic-ray observations and proposes potential interpretations of UHECR composition related to these violations.

Findings

Potential replacement of GZK cutoff with photon or e+ e- pair emission due to Lorentz violation

Discussion of experimental prospects for detecting fundamental principle violations

Analysis of the OPERA neutrino superluminal propagation implications

Abstract

It is not yet clear whether the observed flux suppression for ultra-high energy cosmic rays (UHECR) at energies above \simeq 4.10E19 eV is a signature of the Greisen-Zatsepin-Kuzmin (GZK) cutoff or corresponds, for instance, to the maximum energies available at the relevant sources. Both phenomena can be sensitive to violations of standard special relativity modifying cosmic-ray propagation or acceleration at very high energy, and would in principle allow to set bounds on Lorentz symmetry violation (LSV) parameters. But the precise phenomenological analysis of the experimental data is far from trivial, and other effects can be present. The effective parameters can be directly linked to Planck-scale physics or to physics beyond Planck scale. If a vacuum rest frame (VRF) exists, LSV can modify the internal structure of particles at very high energy. Conventional symmetries may also cease to be valid at energies close to the Planck scale. Other possible violations of fundamental principles and conventional basic hypotheses (quantum mechanics, quark confinement, energy and momentum conservation, vacuum homogeneity and "static" properties, effective space dimensions...) can also be considered and possibly tested in high-energy cosmic-ray experiments. Even below UHE (ultra-high energy), exotic signatures cannot be excluded. We present an updated discussion of the theoretical and phenomenological situation, including prospects for earth-based and space experiments and a simple potential interpretation of the observed UHECR composition in terms of LSV where the GZK cutoff would be replaced by spontaneous emission of photons or e+ e- pairs. As the OPERA result on a possible superluminal propagation of the muon neutrino was announced after the conference, we briefly comment on the consistency problems that a \simeq 2.5 x 10E-5 critical speed anomaly for the muon neutrino can raise.