Bounds for the random walk speed in terms of the Teichm\"uller distance

Abstract

Consider a closed surface $S$ with negative Euler characteristic, and an admissible probability measure on the fundamental group of $S$ with finite first moment with respect to some hyperbolic metric on $S$. Corresponding to each point in Teichm\"uller space there is an associated random walk on the hyperbolic plane. Azemar--Gadre--Gou\"ezel--Haettel--Lessa--Uyanik prove that the drift of this random walk is a proper function on Teichm\"uller space, and that this drift grows at least linearly with respect to the Teichm\"uller distance. In this paper we refine the result. On the one hand, by considering Jenkins-Strebel directions we show that the linear lower bound is sharp. On the other hand, we show that for Lebesgue typical Teichm\"uller geodesics, the drift grows exponentially. We also exhibit Teichm\"uller geodesics for which the growth oscillates between almost linear and exponential. Furthermore, we show that the drift is a quasiconvex function up to a multiplicative constant.