An extended particle with interacting constituents. Pt. 1. Relativistic center of mass

It is shown that a manifestly covariant description of a system of particles can accommodate pairwise scalar interactions without sacrificing the canonical integrity of each particle co-ordinate and its conjugate momentum. The proof requires the introduction of a center-of-mass four-vector co-ordinate. The deduced functional relationship between this center-of-mass proper time and the proper time of each constituent particle yields the expected binding-energy defect for the system rest mass. (author)