Delbruck scattering and the g-factor of a bound electron
  The leading contribution of the light-by-light scattering effects to g-factor of a bound electron is derived. The corresponding amplitude is expressed in terms of low-energy Delbruck scattering of a virtual photon. The result reads Delta g = (7/216) alpha (Z alpha)^5. 
Savely G. Karshenboim (D. I. Mendeleev Institute for Metrology and   Max-Planck-Institut fur Quantenoptik), Alexander I. Mil...