On smooth Feynman propagators for real time path integrals

In this paper we consider various ways of obtaining Feynman propagators that lack the standard highly oscillatory coordinate dependence and discuss their usefulness for Monte Carlo evaluation of the real time path integral. Using truncated basis set expansions to construct appropriate projection operators, we propose simple schemes for incorporating important potential features in the smoothing of a propagator. We point out that the object to be examined in order to determine the efficiency of a particular smoothing scheme is not the shape of the effective propagator itself but rather the product of two such propagators; thus, propagators that appear less oscillatory are not necessarily better behaved. Finally, we discuss the performance of Monte Carlo methods in real time path integral calculations with effective propagators.