Weak Convergence and Banach Space-Valued Functions: Improving the Stability Theory of Feynman's Operational Calculi

In this paper we investigate the relation between weak convergence of a sequence {μn} of probability measures on a Polish space S converging weakly to the probability measure μ and continuous, norm-bounded functions into a Banach space X. We show that, given a norm-bounded continuous function f:S→X, it follows that limn∞ ∫Sf, dμn = ∫Sf, dμ —the limit one has for bounded and continuous real (or complex)—valued functions on S. This result is then applied to the stability theory of Feynman's operational calculus where it is shown that the theory can be significantly improved over previous results.