Searching for Lorentz Violation

TL;DR

This paper reviews various experimental efforts to detect Lorentz violation, discusses theoretical motivations including quantum gravity, and presents new predictions about cosmic-ray energy cutoffs related to Lorentz-violating theories.

Contribution

It provides a comprehensive review of Lorentz violation searches and introduces new theoretical predictions affecting cosmic-ray energy thresholds.

Findings

Potential Lorentz violation detectable by sensitive experiments

Shifted GZK cutoff if fundamental energy is below E_{GZK}

Alternative mechanisms for super-GZK cosmic rays

Abstract

Astrophysical, terrestrial, and space-based searches for Lorentz violation are very briefly reviewed. Such searches are motivated by the fact that all superunified theories (and other theories that attempt to include quantum gravity) have some potential for observable violations of Lorentz invariance. Another motivation is the exquisite sensitivity of certain well-designed experiments and observations to particular forms of Lorentz violation. We also review some new predictions of a specific Lorentz-violating theory: If a fundamental energy \bar{m} in this theory lies below the usual GZK cutoff E_{GZK}, the cutoff is shifted to infinite energy; i.e., it no longer exists. On the other hand, if \bar{m} lies above E_{GZK}, there is a high-energy branch of the fermion dispersion relation which provides an alternative mechanism for super-GZK cosmic-ray protons.