The Furstenberg Poisson Boundary and CAT(0) Cube Complexes

Abstract: We show under weak hypotheses that $\partial X$, the Roller boundary of a finite dimensional CAT(0) cube complex $X$ is the Furstenberg-Poisson boundary of a sufficiently nice random walk on an acting group $\Gamma$. In particular, we show that if $\Gamma$ admits a nonelementary proper action on $X$, and $\mu$ is a generating probability measure of finite entropy and finite first logarithmic moment, then there is a $\mu$-stationary measure on $\partial X$ making it the Furstenberg-Poisson boundary for the $\mu$-random walk on $\Gamma$. We also show that the support is contained in the closure of the regular points. Regular points exhibit strong contracting properties.