New insights into linear maps which are anti-derivable at zero
Authors
Jiankui Li
Antonio M. Peralta
Shanshan Su
Abstract
Let $A$ be a Banach algebra admitting a bounded approximate unit and satisfying property $\mathbb{B}$. Suppose $T: A \rightarrow X$ is a continuous linear map, where $X$ is an essential Banach $A$-bimodule. We prove that the following statements are equivalent:
$(i)$ $T$ is anti-derivable at zero (i.e., $a b =0$ in $A$ $\Rightarrow T(b)\cdot a + b\cdot T(a) =0$);
$(ii)$ There exist an element $ξ\in X^{**}$ and a linear map (actually a bounded Jordan derivation) $d: A\to X$ satisfying $ξ\cdot a = a \cdot ξ\in X$, $T(a) = d(a) +ξ\cdot a$, and $d(b)\cdot a + b\cdot d(a)= - 2 ξ\cdot (b a),$ for all $a,b\in A$ with $a b =0$.
Assuming that $A$ is a C$^*$-algebra we show that a bounded linear mapping $T: A\to X$ is anti-derivable at zero if, and only if, there exist an element $η\in X^{**}$ and an anti-derivation $d: A \rightarrow X$ satisfying $η\cdot a = a \cdot η\in X$, $η\cdot [a,b] = 0$ {\rm(}i.e., $L_η: A \to A$, $L_η (a) = η\cdot a$ vanishes on commutators{\rm)}, and $T(a) = d(a) +η\cdot a$, for all $a,b \in A$. The results are also applied for some special operator algebras.
