Coherent scattering of high-energy photon in a medium
  The coherent scattering of photon in the Coulomb field (the Delbr\"uck scattering) is considered for the momentum transfer $\Delta \ll m$ in the frame of the quasiclassical operator method. In high-energy region this process occurs over rather long distance. The process amplitude is calculated taking into account the multiple scattering of particles of the intermediate electron-positron pair in a medium. The result is the suppression of the process. Limiting cases of weak and strong effects of the multiple scattering are analyzed. The approach used is the generalization of the method developed by authors for consideration of the Landau-Pomeranchuk-Migdal effect. 
V. N. Baier and V. M. Katkov