Random Walks on Homogeneous Spaces by Sparse Solvable Measures

Abstract

The paper analyzes a specific class of random walks on quotients of $X:=\text{SL}(k,{\Bbb R})/ \Gamma$ for a lattice $\Gamma$. Consider a one parameter diagonal subgroup, $\{g_t\}$, with an associated abelian expanding horosphere, $U\cong {\Bbb R}^k$, and let $\phi:[0,1]\rightarrow U$ be a sufficiently smooth curve satisfying the condition that that the derivative of $\phi$ spends $0$ time in any one subspace of ${\Bbb R}^k$. Let $ \mu_U$ be the measure defined as $\phi_*\lambda_{[0,1]},$ where $\lambda_{[0,1]}$ is the Lebesgue measure on $[0,1]$. Let $\mu_A$ be a measure on the full diagonal subgroup of $\text{SL}(k,{\Bbb R})$, such that almost surely the random walk on the diagonal subgroup $A$ with respect to this measure grows exponentially in the direction of the cone expanding $U$. Then the random walk starting at any point $z\in X$, and alternating steps given by $\mu_U$ and $\mu_A$ equidistributes respect to $\text{SL}(k,{\Bbb R})$-invariant measure on $X$. Furthermore, the measure defined by $\mu_A*\mu_U*\dots*\mu_A* \mu_U*\delta_z$ converges exponentially fast to the $\text{SL}(k,{\Bbb R})$-invariant measure on $X$.