Characterization of Lie Derivations on von Neumann Algebras

Let ${\mathcal M}$ be a von Neumann algebra without central summands of type $I_1$ and $ξ\in{\mathbb C}$ a scalar. It is shown that an additive map $L$ on $\mathcal M$ satisfies $L(AB-ξBA)=L(A)B-ξBL(A)+L(B)A-ξAL(B)$ whenever $A,B\in{\mathcal M}$ with $AB=0$ if and only if one of the following statements holds: (1) $ξ=1$, $L=φ+f$, where $φ$ is an additive derivation on $\mathcal M$ and $f$ is an additive map from $\mathcal M$ into its center vanishing on $[A,B]$ with $AB=0$; (2) $ξ=0$, $L(I)\in{\mathcal Z}({\mathcal M})$ and there exists an additive derivation $φ$ such that $L(A)=φ(A)+L(I)A$ for all $A$; (3) $ξ=-1$, $L$ is a Jordan derivation; (4) $ξ$ is rational and $ξ\not=0, \pm1$, $L$ is an additive derivation; (5) $ξ$ is not rational, there exists an additive derivation $φ$ satisfying $φ(ξI)=ξL(I)$ such that $L(A)=φ(A) + L(I)A$ for all $A \in{\mathcal M}$. A linear map $L$ on $\mathcal M$ satisfies $L(AB-ξBA)=L(A)B-ξBL(A)+L(B)A-ξAL(B)$ whenever $A,B\in{\mathcal M}$ with $AB=0$ if and only if there exists a $T\in\mathcal M$ and a linear map $f:{\mathcal M}\rightarrow{\mathcal Z}({\mathcal M})$ vanishing on $[A,B]$ with $AB=0$ such that (i) $ξ=1$, $L(A)=AT-TA+f(A)$ for all $A\in\mathcal M$; (ii) $ξ=0$, $L(I)\in{\mathcal Z}({\mathcal M})$ and $L(A)=AT-(T-L(I))A$ for all $A\in{\mathcal M}$; (iii) $ξ\not=0,1$, $L(A)=AT-TA$ for all $A \in{\mathcal M}$.

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