English

Non-geometric property (T) of warped cones

Group Theory 2025-07-31 v3 Dynamical Systems Operator Algebras

Abstract

In this paper, we study the geometric property (T) for discretized warped cones of an action on a compact Lie group MM by its finitely generated subgroup. We show that if a subgroup GG is dense in MM, then the associated discretized warped cone nM×{t(n)}\bigsqcup_n M\times \{t(n)\} does not have geometric property (T) for any sequence of positive numbers {t(n)}nN\{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,Z[15])SO(d,\mathbb{Z}[\frac{1}{5}]) on SO(d)SO(d) with d5d\geq 5. As an application, we obtain new examples of expanders without geometric property (T), including certain superexpanders.

Keywords

Cite

@article{arxiv.2503.04578,
  title  = {Non-geometric property (T) of warped cones},
  author = {Jintao Deng and Ryo Toyota},
  journal= {arXiv preprint arXiv:2503.04578},
  year   = {2025}
}