Rigidity at infinity for lattices in rank-one Lie groups

TL;DR

This paper extends the Mostow--Prasad rigidity theorem to a broader class of lattices in rank-one Lie groups by introducing a volume notion for representations and analyzing their convergence behavior.

Contribution

It generalizes rigidity results to non-uniform lattices in $PU(p,1)$ and $PSp(p,1)$, establishing convergence of representations with maximal volume to reducible, totally geodesic-preserving limits.

Findings

Sequences of representations with maximal volume converge to reducible, totally geodesic-preserving representations.

The volume notion for representations extends to $PU(m,1)$ and $PSp(m,1)$, enabling generalized rigidity results.

The results apply to non-uniform lattices without torsion in rank-one Lie groups.

Abstract

Let $\Gamma$ be a non-uniform lattice in $PU(p,1)$ without torsion and with $p\geq2 $. We introduce the notion of volume for a representation $\rho:\Gamma \rightarrow PU(m,1)$ where $m \geq p$. We use this notion to generalize the Mostow--Prasad rigidity theorem. More precisely, we show that given a sequence of representations $\rho_n:\Gamma \rightarrow PU(m,1)$ such that $\lim_{n \to \infty} \text{Vol}(\rho_n) =\text{Vol}(M)$, then there must exist a sequence of elements $g_n \in PU(m,1)$ such that the representations $g_n \circ \rho_n \circ g_n^{-1}$ converge to a reducible representation $\rho_\infty$ which preserves a totally geodesic copy of $\mathbb{H}^p_\mathbb{C}$ and whose $\mathbb{H}^p_\mathbb{C}$-component is conjugated to the standard lattice embedding $i:\Gamma \rightarrow PU(p,1) < PU(m,1)$. Additionally, we show that the same definitions and results can be adapted when $\Gamma$ is a non-uniform lattice of $PSp(p,1)$ without torsion and for representations $\rho:\Gamma \rightarrow PSp(m,1)$, still mantaining the hypothesis $m \geq p \geq 2$.