Relativistic quantum mechanics: a space-time formalism for spin-zero particles

A single-particle quantum formalism is constructed for spin-zero particles based upon state functions and operators defined on a four-dimensional space-time manifold. This yields a generalized Schroedinger equation having a Hermitian Hamiltonian and a derivative with respect to proper time. This formulation requires that particle mass be treated as an observable, not as a specified constant. A consistent probability interpretation results and a proper classical limit is exhibited. It is proposed that this formalism should properly replace the conventional Klein-Gordon formalism. (author)