Spontaneous Violation of Lorentz Invariance and Ultra-High Energy Cosmic Rays

Abstract

We propose that local Lorentz invariance is spontaneously violated at high energies, due to a nonvanishing vacuum expectation value of a vector field ϕ^μ, as a possible explanation of the observation of ultra-high energy cosmic rays with an energy above the GZK cutoff. Certain consequences of spontaneous breaking of Lorentz invariance in cosmology are discussed.

12 pages LaTex. No figures. Misprints corrected. Minor changes to equations. References updated. To be published in Int. J. Mod. Phys. D