Predicted properties of Delbrück scattering for photon energies up to104MeV

Using an exact numerical evaluation of the lowest-order Feynman graphs and the impact-factor approximation of Cheng and Wu for the lowest-order as well as the multiphoton-exchange Feynman graphs, properties of Delbrück scattering are investigated at energies between 1 and ${10}^4$ MeV. The predicted scaling behavior starts showing up above about 100 MeV, i.e., at much higher energies than previously anticipated. At angles below 30° the amplitudes are predominantly imaginary and are modified by multiphoton exchange by factors of 2 to 4. At angles above 90° real and imaginary parts are of the same magnitude at all energies. Discrepancies observed between the predictions of the exact numerical evaluation of the lowest-order Feynman graphs and the impact-factor approximation to the lowest-order amplitudes make a reinvestigation of computational methods for the Coulomb-correction effect highly desirable.