Growth in linear groups

Abstract

We prove a conjecture of Helfgott on the structure of sets of bounded tripling in bounded rank, which states the following. Let $A$ be a finite symmetric subset of ${\mathrm{GL}}_n(\mathbf{F})$ for any field $\mathbf{F}$ such that $|A^3|\le K|A|$. Then there are subgroups $H⊴\hat{I}“⊴⟨A⟩$ such that $A$ is covered by $K^{O_n(1)}$ cosets of $\hat{I}“$, $\hat{I}“/H$ is nilpotent of step at most $n-1$, and $H$ is contained in $A^{O_n(1)}$. This theorem includes the Product Theorem for finite simple groups of bounded rank as a special case. As an application of our methods we also show that the diameter of sufficiently quasirandom finite linear groups is poly-logarithmic.

39 pages, final version incorporating referees' corrections, to appear in Duke Math. J