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Noncommutative Function-Theoretic Operator Theory and Applications

✍ Scribed by Joseph A. Ball, Vladimir Bolotnikov


Publisher
Cambridge University Press
Year
2021
Tongue
English
Leaves
439
Series
Cambridge Tracts in Mathematics 225
Edition
1
Category
Library

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✦ Synopsis


This concise monograph explores how core ideas in Hardy space function theory and operator theory continue to be useful and informative in new settings, leading to new insights for noncommutative multivariable operator theory. Beginning with a review of the confluence of system theory ideas and reproducing kernel techniques, the book then covers representations of backward-shift-invariant subspaces in the Hardy space as ranges of observability operators, and representations for forward-shift-invariant subspaces via a Beurling–Lax representer equal to the transfer function of the linear system. This pair of backward-shift-invariant and forward-shift-invariant subspace form a generalized orthogonal decomposition of the ambient Hardy space. All this leads to the de Branges–Rovnyak model theory and characteristic operator function for a Hilbert space contraction operator. The chapters that follow generalize the system theory and reproducing kernel techniques to enable an extension of the ideas above to weighted Bergman space multivariable settings.

✦ Table of Contents


Contents
Preface
Acknowledgments
1 Introduction
1.1 Function-Theoretic Operator Theory on Vectorial Hardy Spaces, Reproducing Kernel Hilbert Spaces, and Discrete-Time Linear Systems: Background
1.2 The Synthesis of the Systems-Theory and Reproducing Kernel Approaches
1.3 StandardWeighted Bergman Spaces
1.4 The Hardy–Fock Space Setting
1.5 Weighted Bergman–Fock Spaces
1.6 Overview
1.7 Notes
2 Formal Reproducing Kernel Hilbert Spaces
2.1 Basic Definitions
2.2 Weighted Hardy–Fock Spaces
2.3 Notes
3 Contractive Multipliers
3.1 Contractive Multipliers in General
3.2 Contractive Multipliers between Hardy-Fock Spaces
3.3 A Noncommutative Leech's Theorem
3.4 Contractive Multipliers from H2U (F + d ) to H2 ω,Y(F + d ) for Admissible ω
3.5 H2 ω,Y(F + d )-Bergman-Inner Formal Power Series
3.6 Notes
4 Stein Relations and Observability Range Spaces
4.1 Preliminaries on Functional Calculus for the Operator BA
4.2 Observability, Defect and Shifted Defect Operators
4.3 Shifted Observability Operators and Observability Gramians
4.4 The Model Shift-Operator Tuple on H^2_ω y (F^+d)
4.5 A Wold Decomposition for ω-Isometric-like Operator Tuples
4.6 Observability-Operator Range Spaces
4.7 Notes
5 Beurling Lax Theorems Based on Contractive Multipliers
5.1 Beurling–Lax Representations with Model Space H2U (F^+_d)
5.2 Beurling-Lax Representations Based on Contractive Multipliers from H^2
{ω',U}(F^+d) to H^2{ω,y}(F^+d)
5.3 Representations with Model Space of the Form \oplus ^n
{j=1} A_{j,U_j} (F^+d)
5.4 Notes
6 Non orthogonal Beurling Lax Representations Based on Wandering Subspaces
6.1 Beurling–Lax Quasi-Wandering Subspace Representations
6.2 Non-orthogonal Beurling–Lax Representations Based on Wandering Subspaces
6.3 Notes
7 Orthogonal Beurling Lax Representations Based on Wandering Subspaces
7.1 Transfer Functions θ
{ω,U_β} and Metric Constraints
7.2 Beurling–Lax Representations Based on Bergman-Inner Families
7.3 Expansive Multiplier Property
7.4 Bergman-Inner Multipliers as Extremal Solutions of Interpolation Problems
7.5 Notes
8 Models for ω-Hypercontractive Operator Tuples
8.1 Model Theory Based on Observability Operators
8.2 The Characteristic Function Approach
8.3 Model Theory for n-Hypercontractions
8.4 Notes
9 Weighted Hardy Fock Spaces Built from a Regular Formal Power Series
9.1 Preliminaries
9.2 The Spaces H^2_{ ω_{p,n},Y}(F^+d) and Their Contractive Multipliers
9.3 Output Stability, Stein Equations, and Inequalities
9.4 The ω
{p,n}, -Shift Model Operator Tuple S_{ω_{p,n},R}
9.5 Observability Operator Range Spaces in H^2_{ω_{p,n},y}(F^+_d)
9.6 Beurling-Lax Theorems Based on Contractive Multipliers
9.7 Beurling-Lax Representations via Quasi-Wandering Subspaces
9.8 Beurling-Lax Representations Based on Bergman-Inner Families
9.9 Operator Model Theory for c.n.c. ∗-(p,n)-Hypercontractive Tuples
9.10 Notes
References
[15]
[32]
[46]
[63]
[82]
[101]
[119]
[140]
[162]
Notation Index
Subject Index


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