Almost invariant half-spaces for operators on Hilbert space. II: operator matrices

This paper is a sequel to [6]. In that paper we transferred the discussions in [1] and [13] concerning almost invariant half-spaces for operators on complex Banach spaces to the context of operators on Hilbert space, and we gave easier proofs of the main results in [1] and [13]. In the present paper we discuss consequences of the above-mentioned results for the matricial structure of operators on Hilbert space

Properties of CC-normal operators (Research on preserver problems on Banach algebras and related topics)

We study various properties of $C$-normal operators, i.e., $T*T$ = $CTT*C$ holds for a conjugation $C$ on $H$. Especially, we show that $T$ − λ$I$ is $C$-normal for all λ ∈ ℂ if and only if $T$ is a complex symmetric operator with the conjugation $C$. In addition, we prove that if $T$ is $C$-normal, then $T$ is normal ⇔ $T$ is quasinormal ⇔ $T$ is hyponormal ⇔ $T$ is $p$-hyponormal for 0 < $p$ ≤ 1. Finally, we investigate equivalent conditions so that Aluthge and Duggal transforms of $C$-normal operators to be $C$-normal operators