English

Actions on classifiable C*-algebras without equivariant property (SI)

Operator Algebras 2024-08-21 v3

Abstract

We exhibit examples of actions of countable discrete groups on both simple and non-simple nuclear stably finite C*-algebras that are tracially amenable but not amenable. We furthermore obtain that, under the additional assumption of strict comparison, amenability is equivalent to tracial amenability plus the equivariant analogue of Matui--Sato's property (SI). By virtue of this equivalence, our construction yields the first known examples of actions on classifiable C*-algebras that do not have equivariant property (SI). We moreover show that such actions can be chosen to absorb the trivial action on the universal UHF algebra, thus showing that equivariant Z\mathcal{Z}-stability does not in general imply equivariant property (SI).

Keywords

Cite

@article{arxiv.2402.16637,
  title  = {Actions on classifiable C*-algebras without equivariant property (SI)},
  author = {Eusebio Gardella and Julian Kranz and Andrea Vaccaro},
  journal= {arXiv preprint arXiv:2402.16637},
  year   = {2024}
}

Comments

10 pages. Minor edits and improvements of the results

R2 v1 2026-06-28T15:00:25.399Z