Abstract
We consider the relationship between derivations d and g of a Banach algebra B that satisfy \({{\sigma}(g(x)) \subseteq {\sigma}(d(x))}\) for every \({x\in B}\) , where σ( . ) stands for the spectrum. It turns out that in some basic situations, say if B = B(X), the only possibilities are that g = d, g = 0, and, if d is an inner derivation implemented by an algebraic element of degree 2, also g = −d. The conclusions in more complex classes of algebras are not so simple, but are of a similar spirit. A rather definitive result is obtained for von Neumann algebras. In general C*-algebras we have to make some adjustments, in particular we restrict our attention to inner derivations implemented by selfadjoint elements. We also consider a related condition \({\|[b,x]\|\leq M\|[a,x]\|}\) for all selfadjoint elements x from a C*-algebra B, where \({a,b\in B}\) and a is normal.
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Brešar, M., Magajna, B. & Špenko, Š. Identifying Derivations Through the Spectra of Their Values. Integr. Equ. Oper. Theory 73, 395–411 (2012). https://doi.org/10.1007/s00020-012-1975-7
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DOI: https://doi.org/10.1007/s00020-012-1975-7