Composition operators on weighted Hardy spaces of polynomial growth

Abstract

In the present paper, we study the composition operators acting on weighted Hardy spaces of polynomial growth, which are concerned with norms, spectra and (semi-)Fredholmness. Firstly, we estimate the norms of the composition operators with symbols of disk automorphisms. Secondly, we discuss the spectra of the composition operators with symbols of disk automorphisms. In particular, it is proven of that the spectrum of a composition operator with symbol of any parabolic disk automorphism is always the unit circle. Thirdly, we consider the Fredholmness of the composition operator $C_{\phi }$ with symbol $\phi$ which is an analytic self-map on the closed unit disk. We prove that $C_{\phi }$ acting on a weighted Hardy space of polynomial growth has closed range (semi-Fredholmness) if and only if $\phi$ is a finite Blaschke product. Furthermore, it is obtained that $C_{\phi }$ is Fredholm if and only if $\phi$ is a disk automorphism.

25 pages, 2 figures