Simple analytical representation for Delbruck scattering amplitudes at high energies

We use a new representation for the semiclassical Green's function of the D irac equation in the Coulomb field to find an exact (in the parameter Z alp ha) expression for the amplitudes of small-angle Delbruck scattering of hig h-energy photons. The values of these amplitudes agree with those obtained in earlier calculations, but the structure of the expressions is much simpl er than that of previously known representations, which makes numerical cal culations much easier. (C) 1999 American Institute of Physics. [S1063-7761( 99)00807-0].