1. A.J. Baltz et al., Phys. Rep. 458, 1 (2008)
2. G. Baur, K. Hencken, D. Trautmann, Phys. Rep. 453, 1 (2007)
3. L.D. Landau, E.M. Lifshitz, Quantenelektrodynamik, Lehrbuch der Theoretischen Physik, No. IV (Akademie Verlag, Berlin, 1986)
4. A.C. Melissinos, in Electromagnetic probes of fundamental physics, Erice, Italy 16–21 October 2001, edited by W. Marciano, S. White (World Scientific, 2003)
5. J.S. Schwinger, Phys. Rev. 76, 790 (1949)