English

Property (T) group factors whose Jones index set equals all positive integers

Operator Algebras 2025-11-11 v2 Group Theory

Abstract

Using a m\'elange of techniques at the rich intersection of deformation/rigidity theory, finite index subfactor theory, and geometric group theory, we prove the existence of a continuum of property (T) factors that are pairwise non-stably isomorphic and whose Jones index sets consist of all positive integers. These factors are realized as group von Neumann algebras L(G)\mathcal{L}(G) associated with property (T) generalized wreath-like product groups GWR(A,BI)G \in \mathscr{WR}(A, B \curvearrowright I) introduced in [CIOS23b], where AA is abelian, BB is a non-parabolic subgroup of a relatively hyperbolic group with residually finite peripheral structure, and BIB \curvearrowright I is a faithful action with infinite orbits. Integer index subfactors of L(G)\mathcal{L}(G) are constructed from extensions of GG. This result advances an open question of P. de la Harpe [dlH95].

Keywords

Cite

@article{arxiv.2511.04822,
  title  = {Property (T) group factors whose Jones index set equals all positive integers},
  author = {Ionut Chifan and Junhwi Lim},
  journal= {arXiv preprint arXiv:2511.04822},
  year   = {2025}
}

Comments

22 pages