Spherically Balanced Hilbert Spaces of Formal Power Series in Several Variables-II

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• 作者：Surjit Kumar
• 关键词：Multi ; shifts ; Slice representation ; Spherical isometry ; Quasi ; similarity ; Von Neumann’s inequality
• 刊名：Complex Analysis and Operator Theory
• 出版年：2016
• 出版时间：March 2016
• 年：2016
• 卷：10
• 期：3
• 页码：505-526
• 全文大小：560 KB
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• 作者单位：Surjit Kumar (1)
  
  1. Department of Mathematics and Statistics, Indian Institute of Technology Kanpur, Kanpur, India
  
• 刊物类别：Mathematics and Statistics
• 刊物主题：Mathematics
  Mathematics
  Operator Theory
  Analysis
  
• 出版者：Birkh盲user Basel
• ISSN：1661-8262

文摘

We continue the study of spherically balanced Hilbert spaces initiated in the first part of this paper. Recall that the complex Hilbert space \(H^2(\beta )\) of formal power series in the variables \(z_1, \ldots , z_m\) is spherically balanced if and only if there exist a Reinhardt measure \(\mu \) supported on the unit sphere \(\partial {\mathbb {B}}\) and a Hilbert space \(H^2(\gamma )\) of formal power series in the variable \(t\) such that $$\begin{aligned} \Vert f\Vert ^2_{H^2(\beta )} = \int _{\partial {\mathbb {B}}}\Vert {f_z}\Vert ^2_{H^2(\gamma )}~d\mu (z)~(f \in H^2(\beta )), \end{aligned}$$where \(f_z(t)=f(t z)\) is a formal power series in the variable \(t\). In the first half of this paper, we discuss operator theory in spherically balanced Hilbert spaces. The first main result in this part describes quasi-similarity orbit of multiplication tuple \(M_z\) on a spherically balanced space \(H^2(\beta ).\) We also observe that all spherical contractive multi-shifts on spherically balanced spaces admit the classical von Neumann’s inequality. In the second half, we introduce and study a class of Hilbert spaces, to be referred to as \({\mathcal {G}}\)-balanced Hilbert spaces, where \({\mathcal {G}}={\mathcal {U}}(r_1) \times {\mathcal {U}}(r_2) \times \cdots \times {\mathcal {U}}(r_k)\) is a subgroup of \({\mathcal {U}}(m)\) with \(r_1 + \cdots + r_k=m.\) In the case in which \({\mathcal {G}}={\mathcal {U}}(m),\) \({\mathcal {G}}\)-balanced spaces are precisely spherically balanced Hilbert spaces. Keywords Multi-shifts Slice representation Spherical isometry Quasi-similarity Von Neumann’s inequality Mathematics Subject Classification Primary 47A13 46E20 47B37 Secondary 47B20 Communicated by Heinrich Begehr.