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 \phi^\mu, 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.

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