Derivations on ideals in commutative $A{W}^{\ast }$-algebras

Abstract

Let $\mathcal{A}$ be a commutative $A{W}^{\ast }$-algebra, let $S(\mathcal{A})$ be the *-algebra of all measurable operators affiliated with $\mathcal{A}$, let $\mathcal{I}$ be an ideal in $\mathcal{A}$, let $s(\mathcal{I})$ be the support of the ideal $\mathcal{I}$ and let $\mathbb{Y}$ be a solid subspace in $S(\mathcal{A})$. The necessary and sufficient conditions of existence of non-zero band preserving derivations from $\mathcal{I}$ to $\mathbb{Y}$ are given. We show that, in case when $\mathbb{Y}\subset \mathcal{A}$, or $\mathbb{Y}$ is a quasi-normed solid space, any band preserving derivation from $\mathcal{I}$ into $\mathbb{Y}$ is always trivial. At the same time, there exist non-zero band preserving derivations from $\mathcal{I}$ with values in $S(\mathcal{A})$, if and only if the Boolean algebra of all projections from the $A{W}^{\ast }$-algebra $s(\mathcal{I})\mathcal{A}$ is not $\sigma$-distributive.

22 pages