Evaluation of Functional Integrals by means of series and the method of Borel transform

Abstract

In this paper I give an evaluation of a functional integral by means of a series in functional derivatives, first of all we propose a differential equation of first order and solve it by iterative methods, to obtain a series for the indefinite integral in one dimension, after that we extend this concept to infinite dimensional spaces, we introduce the functional derivative and propose a functional differential equation for the functional integral which we solve by iteration obtaining a series that includes the n-th order functional derivative dn, this series can be improved by using the Euler transform for alternating series. Also in the second part we study an evaluation of the Path integral using Saddle-point methods, the corrections to the WKB approach that yield to a divergent series are evaluate by means of a Borel transform, to accelerate its convergence we use the Abel-Euler algorithm for power series.