Ultraviolet modified photons and anisotropies in the cosmic microwave   background radiation
  We discuss a minimal canonical modification of electrodynamics in order to account for ultraviolet Lorentz violating effects. This modification creates a birefringence that rotates the polarization planes from different directions. Such effects might be detectable in the anisotropic polarization of the Cosmic Microwave Background radiation. 
J. Gamboa, J. Lopez-Sarrion and A. P. Polychronakos