### Youngsoo Seol (Texas State University - San Marcos)

Title: Random Walks in a sparse random environment

Abstract: We introduce random walks in a sparse random environment on the integer lattice Z and investigate such fundamental asymptotic property of this model as recurrence transience criteria, the existence of the asymptotic speed and a phase transition for its value, limit theorems in both transient and recurrent regimes. The new model combines features of several existing models of random motion in random media and admits a transparent physics interpretation. More specically, the random walk in a sparse random environment can be characterized as a perturbation of the simple random walk by a random potential which is induced by rare "impurities" randomly distributed over the integer lattice. The "impurities" in the media are rigorously dened as a marked point process on Z: The most interesting seems to be the critical (recurrent) case, where Sinai's scaling (log n)^2 for the location of the random walk after n steps is generalized to basically (log n)^alpha; with alpha > 0 being a parameter determined by the distribution of the distance between two successive impurities of the media.