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Automatic continuity of -derivations on -algebras
Authors:Madjid Mirzavaziri   Mohammad Sal Moslehian
Affiliation:Department of Mathematics, Ferdowsi University, P.O. Box 1159, Mashhad 91775, Iran ; Department of Mathematics, Ferdowsi University, P.O. Box 1159, Mashhad 91775, Iran
Abstract:Let $ mathcal{A}$ be a $ C^*$-algebra acting on a Hilbert space $ mathcal{H}$, let $ sigma:mathcal{A}to B(mathcal{H})$ be a linear mapping and let $ d:mathcal{A}to B(mathcal{H})$ be a $ sigma$-derivation. Generalizing the celebrated theorem of Sakai, we prove that if $ sigma$ is a continuous $ *$-mapping, then $ d$ is automatically continuous. In addition, we show the converse is true in the sense that if $ d$ is a continuous $ *$-$ sigma$-derivation, then there exists a continuous linear mapping $ Sigma:mathcal{A}to B(mathcal{H})$ such that $ d$ is a $ *$-$ Sigma$-derivation. The continuity of the so-called $ *$- $ (sigma,tau)$-derivations is also discussed.

Keywords:$*$-$(sigma  tau)$-derivation   $sigma$-derivation   derivation   automatic continuity   $C^*$-algebra
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