Exact Solutions of Bethe-Salpeter Equations with Instantaneous   Interactions
  The Bethe-Salpeter approach allows for quantum-field-theoretic descriptions of relativistic bound states; its inherent complexity, however, usually prevents to find its exact solutions. Under suitable simplifying assumptions about the systems discussed, we derive analytically some examples of rigorous solutions to the instantaneous homogeneous Bethe-Salpeter equation by relating tentative solutions to the interactions responsible for the formation of bound states. 
Wolfgang Lucha and Franz F. Schoberl
hep-ph hep-th nucl-th