On the Power Set of Quasinilpotent Operators in Banach Spaces

Abstract

For a quasinilpotent operator $T$ on a Banach space $X$, Douglas and Yang defined $k_{x}=\limsup\limits_{λ\rightarrow 0}\frac{\ln\|(λ-T)^{-1}x\|}{\ln\|(λ-T)^{-1}\|}$ for each non-zero vector $x$, and called $Λ(T)=\{k_x:x\neq 0\}$ the power set of $T$. In this paper, we prove that $Λ(T)$ always contains $1$ for every quasinilpotent operator $T$ on $X$. Moreover, we introduce the concept of a Banach space $X$ having uniform multiplicity infinity and prove that some classical Banach spaces possess this property. As an application, we show that if $σ\subset [0,1]$ is right closed and contains $1$, then there exists a quasinilpotent operator $T$ on a class of Banach spaces with uniform multiplicity infinity such that $Λ(T)=σ$.