The two-fermion vector potential of constraint theory from Feynman diagrams

Abstract

The relativistic fermion-antifermion bound state vector potential of constraint theory is calculated, in perturbation theory, by means of the Lippmann-Schwinger type equation that relates it to the scattering amplitude. Leading contributions of n-photon exchange diagrams are calculated in an approximation scheme that adapts eikonal approximation to the bound state problem. They produce terms proportional, in three-dimensional x-space, to $(\alpha /r{)}^n$. The series of leading contributions is summed.

Comments: 13 pages, Latex, with three figures included at the end of the article in a Latex file calling the FEYNMAN macropackage