On a characterization of the structured Wolf, Schechter and Browder essential pseudospectra

In this paper, we concern ourselves with essential spectra of an operator AA which is subjected to structured perturbation of the form A⟶A+CDBA⟶A+CDB where BB, CC are given bounded operators and DD is unknown disturbance operator that satisfies ‖D‖<ε‖D‖<ε for a given ε>0ε>0. Thereby, we investigate the structured essential pseudospectra of the sum of two operators acting on a Banach space. Furthermore, we establish characterizations of the structured Schechter essential pseudospectrum of a closed, densely defined linear operator.