Random walks and rank one isometries on CAT(0) spaces

Abstract: Let $G$ be a discrete group, $\mu$ a measure on $G$ and $X$ a proper CAT(0) space. We show that if $G$ acts non-elementarily with a rank one element on $X$, then the pushforward ${Z_n o }n$ to $X$ of the random walk generated by $\mu$ converges almost surely to a rank one point of the boundary. We also show that in this context, there is a unique stationary measure on the visual boundary $\partial\infty X$ of $X$, and that the drift of the random walk is almost surely positive.