Random Walks and Lorentz Processes.

Random walks and Lorentz processes serve as fundamental models for Brownian motion. The study of random walks is a favorite object of probability theory, whereas that of Lorentz processes belongs to the theory of hyperbolic dynamical systems. Here we first present an example where the method based on the probabilistic approach led to new results for the Lorentz process: concretely, the recurrence of the planar periodic Lorentz process with a finite horizon. Afterwards, an unsolved problem-related to a 1981 question of Sinai on locally perturbed periodic Lorentz processes-is formulated as an analogous problem in the language of random walks.