Displaying similar documents to “Spectral characterizations of central elements in Banach algebras”

Commutators of quasinilpotents and invariant subspaces

A. Katavolos, C. Stamatopoulos (1998)

Studia Mathematica

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It is proved that the set Q of quasinilpotent elements in a Banach algebra is an ideal, i.e. equal to the Jacobson radical, if (and only if) the condition [Q,Q] ⊆ Q (or a similar condition concerning anticommutators) holds. In fact, if the inner derivation defined by a quasinilpotent element p maps Q into itself then p ∈ Rad A. Higher commutator conditions of quasinilpotents are also studied. It is shown that if a Banach algebra satisfies such a condition, then every quasinilpotent element...