Within a manifestly covariant formulation of classical dynamics, we characterize the relativistic two-body wave equations admitting a classical analog in which the interaction is realized by means of action at a distance. As an application (and for example) the mass spectrum of Gunion and Li can be obtained from such a classical system, by quantization.

• Received 3 April 1978

DOI:https://doi.org/10.1103/PhysRevD.19.702