English

Integrable measure equivalence and the central extension of surface groups

Metric Geometry 2025-02-18 v2 Group Theory

Abstract

Let Γg\Gamma_g be a surface group of genus g2g\geq 2. It is known that the canonical central extension Γ~g\tilde{\Gamma}_g and the direct product Γg×Z\Gamma_g\times \mathbb{Z} are quasi-isometric. It is also easy to see that they are measure equivalent. By contrast, in this paper, we prove that quasi-isometry and measure equivalence cannot be achieved "in a compatible way". More precisely, these two groups are not uniform (nor even integrable) measure equivalent. In particular, they cannot act continuously, properly and cocompactly by isometries on the same proper metric space, or equivalently they are not uniform lattices in a same locally compact group.

Keywords

Cite

@article{arxiv.1405.2667,
  title  = {Integrable measure equivalence and the central extension of surface groups},
  author = {Kajal Das and Romain Tessera},
  journal= {arXiv preprint arXiv:1405.2667},
  year   = {2025}
}

Comments

15 pages, no figures. In the previous version, we had overlooked a point in the proof of Theorem 1.1. This time we have strengthened this proof and we have added Theorem 1.3