Testing of CP, CPT and causality violation with the light propagation in   vacuum in presence of the uniform electric and magnetic fields
  We have considered the structure of the fundamental symmetry violating part of the photon refractive index in vacuum in the presence of constant electric and magnetic fields. This part of the refractive index can, in principle, contain CPT symmetry breaking terms. Some of the terms violate Lorentz invariance, whereas the others violate locality and causality. Estimates of these effects, using laser experiments are considered. 
S. L. Cherkas, K. G. Batrakov and D. Matsukevich (Institute of Nuclear   Problems, Minsk, Belarus)