English

Property (T) in random quotients of hyperbolic groups at densities above 1/3

Group Theory 2022-03-28 v2

Abstract

We study random quotients of a fixed non-elementary hyperbolic group in the Gromov density model. Let G=S    TG=\langle S\;\vert\; T\rangle be a finite presentation of a non-elementary hyperbolic group, and let Annl,ω(G)Ann_{l,\omega }(G) be the set of elements of norm between lω(l)l-\omega(l) and ll in GG. A random quotient at density dd and length ω\omega-near ll is defined by killing a uniformly randomly chosen set of Sl(G)d\vert S_{l}(G)\vert ^{d} words in Annl,ω(l)(G)Ann_{l,\omega (l)}(G), where ω(l)=ol(l)\omega (l) =o_{l}(l). We prove that for any d>1/3, such a quotient has Property (T) with probability tending to 11 as ll tends to infinity. This result answers a question of Gromov--Ollivier and strengthens a theorem of \.{Z}uk (c.f Kotowski--Kotowski).

Keywords

Cite

@article{arxiv.2202.12318,
  title  = {Property (T) in random quotients of hyperbolic groups at densities above 1/3},
  author = {Calum J. Ashcroft},
  journal= {arXiv preprint arXiv:2202.12318},
  year   = {2022}
}

Comments

39 pages. V2: corrected statement and proof of Theorem A, introduced Theorem B, added appropriate reference for Lemma 4.4