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Dirichlet-type spaces of the unit bidisc and toral 2-isometries

Published online by Cambridge University Press:  15 April 2024

Santu Bera
Affiliation:
Department of Mathematics and Statistics, Indian Institute of Technology Kanpur, Kanpur, India e-mail: santu20@iitk.ac.in
Sameer Chavan*
Affiliation:
Department of Mathematics and Statistics, Indian Institute of Technology Kanpur, Kanpur, India e-mail: santu20@iitk.ac.in
Soumitra Ghara
Affiliation:
Department of Mathematics, Indian Institute of Technology Kharagpur, Kharagpur, India e-mail: soumitra@maths.iitkgp.ac.in

Abstract

We introduce and study Dirichlet-type spaces $\mathcal D(\mu _1, \mu _2)$ of the unit bidisc $\mathbb D^2,$ where $\mu _1, \mu _2$ are finite positive Borel measures on the unit circle. We show that the coordinate functions $z_1$ and $z_2$ are multipliers for $\mathcal D(\mu _1, \mu _2)$ and the complex polynomials are dense in $\mathcal D(\mu _1, \mu _2).$ Further, we obtain the division property and solve Gleason’s problem for $\mathcal D(\mu _1, \mu _2)$ over a bidisc centered at the origin. In particular, we show that the commuting pair $\mathscr M_z$ of the multiplication operators $\mathscr M_{z_1}, \mathscr M_{z_2}$ on $\mathcal D(\mu _1, \mu _2)$ defines a cyclic toral $2$-isometry and $\mathscr M^*_z$ belongs to the Cowen–Douglas class $\mathbf {B}_1(\mathbb D^2_r)$ for some $r>0.$ Moreover, we formulate a notion of wandering subspace for commuting tuples and use it to obtain a bidisc analog of Richter’s representation theorem for cyclic analytic $2$-isometries. In particular, we show that a cyclic analytic toral $2$-isometric pair T with cyclic vector $f_0$ is unitarily equivalent to $\mathscr M_z$ on $\mathcal D(\mu _1, \mu _2)$ for some $\mu _1,\mu _2$ if and only if $\ker T^*,$ spanned by $f_0,$ is a wandering subspace for $T.$

Type
Article
Copyright
© The Author(s), 2024. Published by Cambridge University Press on behalf of Canadian Mathematical Society

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Footnotes

The first author is supported through the PMRF Scheme (2301352), while the work of the third author is supported by INSPIRE Faculty Fellowship (DST/INSPIRE/04/2021/002555).

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