Weighted Cuntz Algebras

Abstract

We study the $C^{\ast }$-algebra $\mathcal{T}/\mathcal{K}$ where $\mathcal{T}$ is the $C^{\ast }$-algebra generated by $d$ weighted shifts on the Fock space of ${\mathbb{C}}^d$, $\mathcal{F}({\mathbb{C}}^d)$, ( where the weights are given by a sequence $\{Z_k\}$ of matrices $Z_k\in M_{d^k}(\mathbb{C})$) and $\mathcal{K}$ is the algebra of compact operators on the Fock space. If $Z_k=I$ for every $k$, $\mathcal{T}/\mathcal{K}$ is the Cuntz algebra ${\mathcal{O}}_d$. We show that $\mathcal{T}/\mathcal{K}$ is isomorphic to a Cuntz-Pimsner algebra and use it to find conditions for the algebra to be simple. We present examples of simple and of non simple algebras of this type. We also describe the $C^{\ast }$-representations of $\mathcal{T}/\mathcal{K}$.

Minor changes. New reference added. To appear in JOT