English

The Poisson boundary of Thompson's group $T$ is not the circle

Dynamical Systems 2025-04-03 v1 Group Theory Probability

Abstract

Let μ\mu be a nondegenerate probability measure with finite entropy on a countable group GHomeo+(S1)G \leq \mathrm{Homeo}_+(S^1) of orientation-preserving homeomorphisms of the circle acting proximally, minimally and topologically nonfreely on S1S^1. We prove that the circle S1S^1 endowed with its unique μ\mu-stationary probability measure is not the Poisson boundary of (G,μ)(G,\mu). When GG is Thompson's group TT and μ\mu is finitely supported, this answers a question posed by B. Deroin [Ergodic Theory Dynam. Systems, 2013] and A. Navas [Proceedings of the International Congress of Mathematicians, 2018].

Keywords

Cite

@article{arxiv.2504.01283,
  title  = {The Poisson boundary of Thompson's group $T$ is not the circle},
  author = {Martín Gilabert Vio and Cosmas Kravaris and Eduardo Silva},
  journal= {arXiv preprint arXiv:2504.01283},
  year   = {2025}
}