High-Energy Tests of Lorentz Invariance

We develop a perturbative framework with which to discuss departures from exact Lorentz invariance and explore their potentially observable ramifications. Tiny non-invariant terms introduced into the standard model Lagrangian are assumed to be renormalizable (dimension $\le 4$), invariant under $SU(3)\otimes SU(2)\otimes U(1)$ gauge transformations, and rotationally and translationally invariant in a preferred frame. There are a total of 46 independent TCP-even perturbations of this kind, all of which preserve anomaly cancellation. They define the energy-momentum eigenstates and their maximal attainable velocities in the high-energy limit. The effects of these perturbations increase rapidly with energy in the preferred frame, more rapidly than those of TCP-odd perturbations. Our analysis of Lorentz-violating kinematics reveals several striking new phenomena that are relevant both to cosmic-ray physics ({\it e.g.,} by undoing the GZK cutoff) and neutrino physics ({\it e.g.,} by generating novel types of neutrino oscillations). These may lead to new and sensitive high-energy tests of special relativity.