Splitting of a high-energy photon in a strong Coulomb field

The helical splitting amplitudes of a high-energy photon in an external Coulomb field are found exactly with respect to Zα. Both screened and unscreened potentials are investigated. The treatment is carried out within the semiclassical approach, which is valid for small angles between the momenta of all photons. A new representation is used for the semiclassical electronic Green’s function. The resulting expressions are analyzed in detail for...