Probabilistic characterizations of essential self-adjointness and removability of singularities

We consider the Laplacian and its fractional powers of order less than one on the complement R� \ Σ of a given compact set Σ C R� of zero Lebesgue measure. Depending on the size of Σ, the operator under consideration, equipped with the smooth compactly supported functions on R� \ Σ, may or may not be essentially self-ajoint. We survey well-known descriptions for the critical size of Σ in terms of capacities and Hausdorff measures. In addition, we collect some known results for certain two-parameter stochastic processes. What we finally want to point out is, that, although a priori essential self-adjointness is not a notion directly related to classical probability, it admits a characterization via Kakutani-type theorems for such processes.