About the connection between vacuum birefringence and the light-light   scattering amplitude
  Birefringence phenomena stemming from vacuum polarization are revisited in the framework of coherent scattering. Based on photon-photon scattering, our analysis brings out the direct connection between this process and vacuum birefringence. We show how this procedure can be extended to the Kerr and the Cotton-Mouton birefringences in vacuum, thus providing a unified treatment of various polarization schemes, including those involving static fields. 
J. Haissinski, S. Dagoret, M. Urban and F. Zomer