Consequences of vacuum polarization on electromagnetic waves in a   Lorentz-symmetry breaking scenario
  The propagation of electromagnetic waves in a Lorentz-symmetry violating scenario where there is a region of polarized vacuum is studied. It turns out that the photon field acquires an interesting polarization state, possibly useful to set up upper bounds in Lorentz-violating models at laboratory scales. 
B. Agostini, F. A. Barone, F. E. Barone, Patricio Gaete and J. A.   Helay\"el-Neto
hep-th