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JOURNALS // Algebra i Analiz // Archive

Algebra i Analiz, 2007 Volume 19, Issue 3, Pages 76–105 (Mi aa120)

This article is cited in 4 papers

Research Papers

$J_{p,m}$-inner dilations of matrix-valued functions that belong to the Carathódory class and admit pseudocontinuation

D. Z. Arov, N. A. Rozhenko

South Ukrainian State Pedagogical University, Odessa

Abstract: The class $\ell^{p\times p}$ of matrix-valued functions $c(z)$ holomorphic in the unit disk $D=\{{z\in\mathbb{C}:|z|<1}\}$, having order $p$, and satisfying $\operatorname{Re}c(z)\ge 0$ in $D$ is considered, as well as its subclass $\ell^{p\times p}\Pi$ of matrix-valued functions $c(z)\in \ell^{p\times p}$ that have a meromorphic pseudocontinuation $c_-(z)$ to the complement $D_e=\{z\in\mathbb{C}:1<|z|\le\infty\}$ of the unit disk with bounded Nevanlinna characteristic in $D_e$.
For matrix-valued functions $c(z)$ of class $\ell^{p\times p}\Pi$ a representation as a block of a certain $J_{p,m}$-inner matrix-valued function $\theta(z)$ is obtained. The latter function has a special structure and is called the $J_{p,m}$-inner dilation of $c(z)$. The description of all such representations is given.
In addition, the following special $J_{p,m}$-inner dilations are considered and described: minimal, optimal, $*$-optimal, minimal and optimal, minimal and $*$-optimal. Also, $J_{p,m}$-inner dilations with additional properties are treated: real, symmetric, rational, or any combination of them under the corresponding restrictions on the matrix-valued function $c(z)$. The results extend to the case where the open upper half-plane $\mathbb{C}_+$ is considered instead of the unit disk $D$. For entire matrix-valued functions $c(z)$ with $\operatorname{Re}c(z)\ge 0$ in $\mathbb{C_+}$ and with Nevanlinna characteristic in $\mathbb{C}_-$, the $J_{p,m}$-inner dilations in $\mathbb{C}_+$ that are entire matrix-valued functions are also described.

Keywords: Holomorphic matrix-valued functions, dilations, pseudocontinuation.

MSC: 20G35

Received: 09.11.2006


 English version:
St. Petersburg Mathematical Journal, 2008, 19:3, 375–395

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