Pseudo-Fredholm operators form a regularity on Hilbert spaces

Abstract

Let $H$ be a complex Hilbert space. We prove that the class of pseudo-Fredholm operators on $H$ is a regularity in the sense of Kordula and Müller. We also prove that the classes of left and right generalized Drazin invertible operators are regularities on $H$. Consequently, the generalized Kato spectrum and the corresponding generalized Drazin spectra satisfy the spectral mapping theorem. We construct an operator $T$ on a separable complex Banach space such that $T^2$ is right generalized Drazin invertible whereas $T$ is not pseudo-Fredholm. In particular, the power axiom need not hold for pseudo-Fredholm operators on Banach spaces. Finally, we show that the accumulation sets of the approximate point and surjectivity spectra define regularities on Banach spaces, yielding another proof of the regularity of generalized Drazin invertible operators in \B(X).