Uniform Kazhdan Constant for some families of linear groups

Abstract

Let $R$ be a ring generated by $l$ elements with stable range $r$. Assume that the group $EL_d(R)$ has Kazhdan constant $ε_0>0$ for some $d > r $. We prove that there exist $ε(ε_0,l) >0$ and $k \in N$, s.t. for every $n \geq d$, $EL_n(R)$ has a generating set of order $k$ and a Kazhdan constant larger than $ε$. As a consequence, we obtain for $SL_n(Z)$ where $n \geq 3$, a Kazhdan constant which is independent of $n$ w.r.t generating set of a fixed size.