On the norm of idempotents in C*-algebras

Abstract

In this paper we study norms of idempotents in C*-algebras. Results of Ljance, Vidav, Buckholtz and Wimmer on idempotent operators in Hilbert spaces are considered in the setting of C*-algebras, and simpler new proofs, based on algebraic and spectral rather than spatial arguments, are given. We give an application to projections with respect to a-involutions. © 2004 Rocky Mountain Mathematics Consortium.