Department of Applied Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152, Japan ; Department of Applied Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152, Japan
Abstract:
This paper establishes a criterion for whether a -dimensional random walk on the integer lattice visits a space-time subset infinitely often or not. It is a precise analogue of Wiener's test for regularity of a boundary point with respect to the classical Dirichlet problem. The test obtained is applied to strengthen the harder half of Kolmogorov's test for the random walk.