Abstract
We consider a random walk on a homogeneous space $G/\Lambda$ where $G$ is $\mathrm{SO}(2,1)$ or $\mathrm{SO}(3,1)$ and $\Lambda$ is a lattice. The walk is driven by a probability measure $\mu$ on $G$ whose support generates a Zariski-dense subgroup.
We show that for every starting point $x\in G/\Lambda$ which is not trapped in a finite $\mu$-invariant set, the $n$-step distribution $\mu^{*n}*\delta_x$ of the walk equidistributes toward the Haar measure. Moreover, under arithmetic assumptions on the pair $(\Lambda,\mu)$, we show the convergence occurs at an exponential rate, tempered by the obstructions that $x$ may be high in a cusp or close to a finite orbit.
Our approach is substantially different from that of Benoist–Quint [13], whose equidistribution statements only hold in Cesàro average and are not quantitative, that of Bourgain-Furman-Lindenstrauss-Mozes [21] concerning the torus case, and that of Lindenstrauss-Mohammadi-Wang and Yang [57, 77, 59] about the analogous problem for unipotent flows. A key new feature of our proof is the use of a new phenomenon with we call multi slicing. The latter is a generalization of the discretized project theorems à la Bourgain and we believe it presents independent interest.
