Higher Brin--Thompson groups are Kazhdan

Abstract

We give an algebraic criterion for certain sequences $(G_n{)}_{n\in \mathbb{N}}$ of groups to have Kazhdan's property $(T)$ eventually. As a consequence, we prove that the Brin--Thompson groups $nV$ have Kazhdan's property $(T)$ for large $n$. The algebraic criterion provides a uniform proof that $nV$, $\mathrm{Aut}(F_n)$ and ${\mathrm{EL}}_n(R)$ for a finitely generated associative unital ring $R$ have property $(T)$ for large $n$. In an appendix, written by Francesco Fournier-Facio, it is shown that the group $nV$ for large $n$ is neither hyperlinear, in particular not sofic, nor $\mathrm{MF}$. Further, it is not Schatten $p$-approximable for any $1\le p<\infty$.

arXiv commentMain paper by Roman Sauer and Eduard Schesler, with an appendix by Francesco Fournier-Facio. v2: minor changes