The essential spectrum, norm, and spectral radius of abstract multiplication operators

Abstract

Abstract Let E E be a complex Banach lattice and T T is an operator in the center Z ( E ) = { T : ∣ T ∣ ≤ λ I for some λ } Z\left(E)=\left\{T:| T| \le \lambda I\hspace{0.33em}\hspace{0.1em}\text{for some}\hspace{0.1em}\hspace{0.33em}\lambda \right\} of E E . Then, the essential norm ‖ T ‖ e \Vert T{\Vert }_{e} of T T equals the essential spectral radius r e ( T ) {r}_{e}\left(T) of T T . We also prove r e ( T ) = max { ‖ T A d ‖ , r e ( T A ) } {r}_{e}\left(T)=\max \left\{\Vert {T}_{}\hspace{-0.35em}{}_{{A}^{d}}\Vert ,{r}_{e}\left({T}_{A})\right\} , where T A {T}_{A} is the atomic part of T T and T A d {T}_{}\hspace{-0.35em}{}_{{A}^{d}} is the nonatomic part of T T . Moreover, r e ( T A ) = limsup ℱ λ a {r}_{e}\left({T}_{A})={\mathrm{limsup}}_{{\mathcal{ {\mathcal F} }}}{\lambda }_{a} , where ℱ {\mathcal{ {\mathcal F} }} is the Fréchet filter on the set A A of all positive atoms in E E of norm one and λ a {\lambda }_{a} is given by T A a = λ a a {T}_{A}a={\lambda }_{a}a for all a ∈ A a\in A .