Maximal numerical range and quadratic elements in a C✻-algebra
El Hassan Benabdi, Mohamed Barraa, M. K. Chraibi, Abderrahim Baghdad · Operators and Matrices · 2021
In this paper, we give a description of the maximal numerical range of a hyponormal element and a characterization of a normaloid element in a C * -algebra. We also give an explicit formula for the maximal numerical range of a quadratic operator acting on a complex Hilbert space. As a consequence, we determine the maximal numerical range of a rank-one operator.