On the Dirichlet space for finitely connected regions

Author:
Kit Chak Chan

Journal:
Trans. Amer. Math. Soc. **319** (1990), 711-728

MSC:
Primary 46E20; Secondary 30H05, 47B38

MathSciNet review:
958885

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Abstract: This paper is devoted to the study of the Dirichlet space for finitely connected regions ; we are particularly interested in the algebra of bounded multiplication operators on this space. Results in different directions are obtained. One direction deals with the structure of closed subspaces invariant under all bounded multiplication operators. In particular, we show that each such subspace contains a bounded function. For regions with circular boundaries we prove that a finite codimensional closed subspace invariant under multiplication by must be invariant under all bounded multiplication operators, and furthermore it is of the form , where is a polynomial with all its roots lying in . Another direction is to study cyclic and noncyclic vectors for the algebra of all bounded multiplication operators. Typical results are: if and is bounded away from zero then is cyclic; on the other hand, if the zero set of the radial limit function of on the boundary has positive logarithmic capacity, then is not cyclic. Also, some other sufficient conditions for a function to be cyclic are given. Lastly, we study transitive operator algebras containing all bounded multiplication operators; we prove that they are dense in the algebra of all bounded operators in the strong operator topology.

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Additional Information

DOI:
http://dx.doi.org/10.1090/S0002-9947-1990-0958885-4

Keywords:
Dirichlet space,
finitely connected region,
multiplication operators,
invariant subspaces,
cyclic vectors,
transitive operator algebras,
logarithmic capacity

Article copyright:
© Copyright 1990
American Mathematical Society