Generalized Kato decomposition, Kato type decomposition and various types of spectra
Snežana Č. Živković-Zlatanović, Miloš Cvetković
Abstract
Snežana Č. Živković-Zlatanović, Miloš Cvetković
Abstract
Let ${\bf R}$ denote any of the following classes: invertible operators, bounded below operators, surjective operators, upper (lower) semi-Fredholm operators, Fredholm operators, upper (lower) semi-Browder operators, Browder operators, upper (lower) semi-Weyl operators, Weyl operators. For a bounded linear operator $T$ on a Banach space $X$ we show that $T=T_M\oplus T_N$ with $T_M \in {\bf R}$ and $T_N$ quasinilpotent (nilpotent) if and only if $T$ admits a generalized Kato decomposition ($T$ is of Kato type) and $0$ is not an interior point of the corresponding spectrum $\sigma_{\bf R}(T)=\{\lambda \in \mathbb{C}: T-\lambda \notin {\bf R}\}$. As an application we obtain that every non-isolated boundary point of the spectrum $\sigma_{\bf R}(T)$ belongs to the generalized Kato spectrum of $T$. In addition, we prove that the boundary of the generalized Drazin spectrum of $T$ is contained in the generalized Kato spectrum of $T$ and also, the boundary of the Drazin spectrum of $T$ is contained in the Kato type spectrum of $T$.
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Let ${\bf R}$ denote any of the following classes: invertible operators, bounded below operators, surjective operators, upper (lower) semi-Fredholm operators, Fredholm operators, upper (lower) semi-Browder operators, Browder operators, upper (lower) semi-Weyl operators, Weyl operators. For a bounded linear operator $T$ on a Banach space $X$ we show that $T=T_M\oplus T_N$ with $T_M \in {\bf R}$ and $T_N$ quasinilpotent (nilpotent) if and only if $T$ admits a generalized Kato decomposition ($T$ is of Kato type) and $0$ is not an interior point of the corresponding spectrum $\sigma_{\bf R}(T)=\{\lambda \in \mathbb{C}: T-\lambda \notin {\bf R}\}$. As an application we obtain that every non-isolated boundary point of the spectrum $\sigma_{\bf R}(T)$ belongs to the generalized Kato spectrum of $T$. In addition, we prove that the boundary of the generalized Drazin spectrum of $T$ is contained in the generalized Kato spectrum of $T$ and also, the boundary of the Drazin spectrum of $T$ is contained in the Kato type spectrum of $T$.
Key concepts: Mathematics, Spectrum (functional analysis), Surjective function, Type (biology), Bounded function, Boundary (topology), Bounded operator, Operator (biology)