English

Normal weighted composition operators on the Hardy space

Functional Analysis 2009-10-08 v1

Abstract

Let g be an analytic function on the open unit disc U such that g(U) is contained in U, and let h be an analytic function on U such that the weighted composition operator W_{h,g) defined by W_{h,g}f = h f(g) is bounded on the Hardy space H^2. We characterize those weighted composition operators on H^2 that are unitary, showing that in contrast to the unweighted case (h=1), every automorphism of U induces a unitary weighted composition operator. A conjugation argument, using these unitary operators, allows us to describe all normal weighted composition operators on H^2 for which the inducing map g fixes a point in U. This description shows both h and g must be linear fractional in order for W_{h,g} to be normal (assuming g fixes a point in U). In general, we show that if W_{h, g} is normal on H^2 and h is not the zero function, then g must be either univalent on U or constant. Descriptions of spectra are provided for the operator W_{h,g} when it is unitary or when it is normal and g fixes a point in U.

Keywords

Cite

@article{arxiv.0910.1259,
  title  = {Normal weighted composition operators on the Hardy space},
  author = {Paul S. Bourdon and Sivaram K. Narayan},
  journal= {arXiv preprint arXiv:0910.1259},
  year   = {2009}
}

Comments

11 pages

R2 v1 2026-06-21T13:55:16.436Z