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arXiv · 2503.04578

Non-geometric property (T) of warped cones

Jintao Deng·Ryo Toyota
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Abstract

In this paper, we study the geometric property (T) for discretized warped cones of an action on a compact Lie group $M$ by its finitely generated subgroup. We show that if a subgroup $G$ is dense in $M$, then the associated discretized warped cone $\bigsqcup_n M\times \{t(n)\}$ does not have geometric property (T) for any sequence of positive numbers $\{t(n)\}_{n\in \mathbb{N}}$ converging to $\infty$. This result applies to certain ergodic actions of groups with property (T), for example, the action of $SO(d,\mathbb{Z}[\frac{1}{5}])$ on $SO(d)$ with $d\geq 5$. As an application, we obtain new examples of expanders without geometric property (T), including certain superexpanders.

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Jintao Deng, Ryo Toyota. 2025-07-30. Non-geometric property (T) of warped cones. https://arxiv.org/abs/2503.04578

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