Generalized Friedland’s theorem for C0-semigroups

Friedland’s characterization of bounded normal operators is shown to hold for infinitesimal generators of C0-semigroups. New criteria for normality of bounded operators are furnished in terms of Hamburger moment problem. All this is achieved with the help of the celebrated Ando’s theorem on paranormal operators. © 2008 Elsevier Inc. All rights reserved.