HIGH-ENERGY PHOTON SPLITTING ON HEAVY-ATOMS

The helicity amplitudes of high-energy photon splitting in an external Coulomb field are obtained exactly in the parameter Z alpha. The cons ideration is based on the quasiclassical approach, valid for small ang les between all photon momenta. A new representation of the quasiclass ical electron Green function is exploited. General expressions obtaine d are analyzed in detail when the transverse momenta of both final pho tons are much larger than the electron mass. It is shown that, at Z al pha similar to 1. Coulomb corrections essentially change the cross sec tion as compared to the Born approximation. Screened and unscreened po tentials are considered.