Jordan derivations on semiprime rings

Abstract

I. N. Herstein has proved that any Jordan derivation on a 2 2 -torsion free prime ring is a derivation. In this paper we prove that Herstein’s result is true in 2 2 -torsion free semiprime rings. This result makes it possible for us to prove that any linear Jordan derivation on a semisimple Banach algebra is continuous, which gives an affirmative answer to the question posed by A. M. Sinclair in [5].