Sublinear Rigidity of Lattices in Semisimple Lie Groups

Abstract

Let $G$ be a real centre-free semisimple Lie group without compact factors. I prove that irreducible lattices in $G$ are rigid under two types of sublinear distortions. The first result is that the class of lattices in groups that do not admit $\mathbb{R}$-rank $1$ factors is $\textit{SBE complete}$: if $\Lambda$ is an abstract finitely generated group that is Sublinearly BiLipschitz Equivalent (SBE) to a lattice $\Gamma\leq G$, then $\Lambda$ can be homomorphically mapped into $G$ with finite kernel and image a lattice in $G$. For such $G$ this generalizes the well known quasi-isometric completeness of lattices. The second result concerns sublinear distortions within $G$ itself, and holds without any restriction on the rank of the factors: if $\Lambda\leq G$ is a discrete subgroup that $\textit{sublinearly covers}$ a lattice $\Gamma\leq G$, then $\Lambda$ is itself a lattice.