Optimal Littlewood-Offord inequalities in groups

Abstract

We prove several Littlewood-Offord type inequalities for arbitrary groups. In groups having elements of finite order the worst case scenario is provided by the simple random walk on a certain cyclic subgroup. The inequalities we obtain are optimal if the underlying group contains an element of certain order. It turns out that for torsion-free groups Erd\H{o}s's bound still holds. Our results strengthen and generalize some very recent results by Tiep and Vu.