Relativistic, 3-Dimensional, 2-Body Integral Equations. On-Shell and Off-Shell Formalisms

Abstract

Covariant on-shell and off-shell formalisms are presented on the basis of the Bethe-Salpeter equation and the 2-particle unitarity condition. The 2-body theory is formulated in terms of the relativistic 3-dimensional integral equations of the Low type. Three approaches are presented which take into account differently the left-hand cuts, besides including the 2-particle right-hand cut. The partial-wave expansion and some methods of solving the reduced equations are pointed out. A covariant formulation and a generalization for arbitrary masses are included in full detail.