HOW TO OBTAIN A COVARIANT BREIT TYPE EQUATION FROM RELATIVISTIC CONSTRAINT THEORY

It is shown that, by an appropriate modification of the structure of t he interaction potential, the Breit equation can be incorporated into a set of two compatible manifestly covariant wave equations, derived f rom the general rules of constraint theory. The complementary equation to the covariant Breit type equation determines the evolution law in the relative time variable. The interaction potential can be systemati cally calculated in perturbation theory from Feynman diagrams. The nor malization condition of the Breit wavefunction is determined. The wave equation is reduced, for general classes of potential, to a single Pa uli-Schrodinger-type equation. As an application of the covariant Brei t type equation, we exhibit massless pseudoscalar bound-state solution s, corresponding to a particular class of confining potentials.