Random walks on solvable matrix groups

Abstract

We define matrix groups $FG_n(P)$ for each natural number $n$ and finite set of primes $P$, such that every rational-valued upper triangular matrix group is a (possibly distorted) subgroup. Brofferio and Schapira [Brofferio2011poisson], described the \PF boundary of $GL_n (\mathbb{Q})$ for measures of finite first moment with respect to adelic length. We show that adelic length is a word metric estimate on $FG_n(P)$ by constructing another, intermediate, word metric estimate which can be easily computed from the entries of any matrix in the group. In particular, finite first moment of a probability measure with respect to adelic length is an equivalent condition to requiring finite first moment with respect to word length in $FG_n(P)$. We also investigate random walks in the case that $P$ is a length one sequence. Conditions for pointwise convergence in $\mathbb{R}$ or $\mathbb{Q}_p$ are given. When these conditions are satisfied, we give path estimates from boundary points, discuss boundary triviality, show that the resulting space is a $\mu$-boundary and give cases where the $\mu$-boundary is the \PF boundary, as conjectured by Kaimanovich.