Hostname: page-component-cd9895bd7-q99xh Total loading time: 0 Render date: 2024-12-26T20:37:24.606Z Has data issue: false hasContentIssue false

Universal Blaschke products

Published online by Cambridge University Press:  15 January 2004

PAMELA GORKIN
Affiliation:
Department of Mathematics, Bucknell University, PA 17837, Lewisburg, U.S.A. e-mail: pgorkin@bucknell.edu
RAYMOND MORTINI
Affiliation:
Département de Mathématiques, Université de Metz, Ile du Saulcy, F-57045 Metz, France. e-mail: mortini@poncelet.univ-metz.fr

Abstract

We extend a result of M. Heins by showing that for any sequence of points $(z_n)$ in the unit disk ${\Bbb D}$ tending to the boundary, there is a Blaschke product $B$ which is universal for noneuclidian translates in the sense that the set $\{B((z\,{+}\,z_n)/(1\,{+}\,\overline{z}_nz))\,{:} n\,{\in}\,{\Bbb N}\}$ is locally uniformly dense in the set of all holomorphic functions bounded by one on ${\Bbb D}$. From this, we conclude that for every countable set ${\sp L}$ of hyperbolic/parabolic automorphisms of the unit disk there exists a Blaschke product which is a common cyclic vector in $H^2$ for the composition operators associated with the elements in ${\sp L}$. These results are obtained by transferring the associated approximation problems to interpolation problems on the corona of $H^\infty$.

Type
Research Article
Copyright
2004 Cambridge Philosophical Society

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)