On closed Lie ideals of certain tensor products of $C^*$-algebras

Abstract

For a simple $C^*$-algebra $A$ and any other $C^*$-algebra $B$, it is proved that every closed ideal of $A \otimes^{\min} B$ is a product ideal if either $A$ is exact or $B$ is nuclear. Closed commutator of a closed ideal in a Banach algebra whose every closed ideal possesses a quasi-central approximate identity is described in terms of the commutator of the Banach algebra. If $\alpha$ is either the Haagerup norm, the operator space projective norm or the $C^*$-minimal norm, then this allows us to identify all closed Lie ideals of $A \otimes^{\alpha} B$, where $A$ and $B$ are simple, unital $C^*$-algebras with one of them admitting no tracial functionals, and to deduce that every non-central closed Lie ideal of $B(H) \otimes^{\alpha} B(H)$ contains the product ideal $K(H) \otimes^{\alpha} K(H)$. Closed Lie ideals of $A \otimes^{\min} C(X)$ are also determined, $A$ being any simple unital $C^*$-algebra with at most one tracial state and $X$ any compact Hausdorff space. And, it is shown that closed Lie ideals of $A \otimes^{\alpha} K(H)$ are precisely the product ideals, where $A$ is any unital $C^*$-algebra and $\alpha$ any completely positive uniform tensor norm.