On $q$-tensor products of Cuntz algebras

TL;DR

This paper studies a family of $C^*$-algebras called $\\mathcal{E}_{n,m}^q$, showing that their structure remains unchanged under certain deformations and providing explicit descriptions of their ideals and isomorphism classes.

Contribution

It provides explicit formulas for untwisting $q$-deformations of Cuntz-Toeplitz algebras and characterizes their ideal structure, demonstrating invariance of their isomorphism class across deformations.

Findings

Isomorphism class of $\mathcal{E}_{n,m}^q$ does not depend on $q$ for $|q|<1$ or $|q|=1$.

Explicit description of all ideals in $\mathcal{E}_{n,m}^q$ for $|q|=1$.

Identification of the quotient algebra with a Rieffel deformation.

Abstract

We consider the $C^*$-algebra $\mathcal{E}_{n,m}^q$, which is a $q$-twist of two Cuntz-Toeplitz algebras. For the case $|q|<1$, we give an explicit formula which untwists the $q$-deformation showing that the isomorphism class of $\mathcal{E}_{n,m}^q$ does not depend on $q$. For the case $|q|=1$, we give an explicit description of all ideals in $\mathcal{E}_{n,m}^q$. In particular, we show that $\mathcal{E}_{n,m}^q$ contains a unique largest ideal $\mathcal{M}_q$. We identify $\mathcal{E}_{n,m}^q / \mathcal{M}_q$ with the Rieffel deformation of $\mathcal{O}_n \otimes \mathcal{O}_m$ and use a K-theoretical argument to show that the isomorphism class does not depend on $q$. The latter result holds true in a more general setting of multiparameter deformations.