Quantum BRST properties of reparametrization invariant theories

Any regular quantum mechanical system may be cast into an abelian gauge theory by simply reformulating it as a reparametrization invariant theory. We present a detailed study of the BRST quantization of such reparametrization invariant theories within a precise operator version of BRST. The treatment elucidates several intricate aspects of the BRST quantization of reparametrization invariant theories like the appearance of physical time. We propose general rules for how physical wave functions and physical propagators are to be projected from the BRST singlets and propagators in the ghost extended BRST theory. These projections are performed by boundary conditions which are precisely specified by the operator BRST. We demonstrate explicitly the validity of these rules for the considered class of models. The corresponding path integrals are worked out explicitly and compared with the conventional BFV path integral formulation.