We characterize Yang-Mills connections in vector bundles in terms of covariant derivatives of stochastic parallel transport along variations of Brownian bridges on the base manifold. In particular, we prove that a connection in a vector bundle E is Yang-Mills if and only if the covariant derivative of parallel transport along Brownian bridges (in the direction of their drift) is a local martingale, when transported back to the starting point. We present a Taylor expansion up to order 3 for stochastic parallel transport in E along small rescaled Brownian bridges and prove that the connection in E is Yang-Mills if and only if all drift terms in the expansion (up to order 3) vanish or, equivalently, if and only if the average rotation of parallel transport along small bridges and loops is of order 4.
Introduction.This article is concerned with the characterization of YangMills connections in a vector bundle E over a compact Riemannian manifold M in terms of stochastic parallel transport along Brownian bridges. Recall that YangMills connections in a vector bundle E with a metric over M are the critical points of the following functional (the so-called Yang-Mills action):