English

Finite groups acting on higher dimensional noncommutative tori

Operator Algebras 2014-06-03 v2

Abstract

For the canonical action α\alpha of SL2(Z)\operatorname{SL}_2(\mathbb{Z}) on 2-dimensional simple rotation algebras Aθ\mathcal{A}_\theta, it is known that if FF is a finite subgroup of SL2(Z)\operatorname{SL}_2(\mathbb{Z}), the crossed products AθαF\mathcal{A}_\theta\rtimes_\alpha F are all AF algebras. In this paper we show that this is not the case for higher dimensional noncommutative tori. More precisely, we show that for each n3n\geq 3 there exist noncommutative simple ϕ(n)\phi(n)-dimensional tori AΘ\mathcal{A}_\Theta which admit canonical action of Zn\mathbb{Z}_n and for each odd n7n\geq 7 with 2ϕ(n)n+52\phi(n)\geq n+5 their crossed products AΘαZn\mathcal{A}_\Theta\rtimes_\alpha \mathbb{Z}_n are not AF (with nonzero K1K_1-groups). It is also shown that the only possible canonical action by a finite group on a 33-dimensional simple torus is the flip action by Z2\mathbb{Z}_2. Besides, we discuss the canonical actions by finite groups Z5,Z8,Z10\mathbb{Z}_5, \mathbb{Z}_8, \mathbb{Z}_{10}, and Z12\mathbb{Z}_{12} on the 44-dimensional torus of the form AθAθ\mathcal{A}_\theta\otimes \mathcal{A}_\theta.

Keywords

Cite

@article{arxiv.1402.1826,
  title  = {Finite groups acting on higher dimensional noncommutative tori},
  author = {Ja A Jeong and Jae Hyup Lee},
  journal= {arXiv preprint arXiv:1402.1826},
  year   = {2014}
}

Comments

25 pages

R2 v1 2026-06-22T03:04:00.169Z