Singular unitary dilations |
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Authors: | Wu Pei Yuan Takahashi Katsutoshi |
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Institution: | (1) Department of Applied Mathematics, National Chiao Tung University, Hsinchu, Taiwan Republic of China;(2) Department of Mathematics, University of Hokkaido, Sapporo, Hokkaido, Japan |
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Abstract: | We study the problem of determining which bounded linear operator on a Hilbert space can be dilated to a singular unitary operator. Some of the partial results we obtained are (1) every strict contraction has a diagonal unitary dilation, (2) everyC
0 contraction has a singular unitary dilation, and (3) a contraction with one of its defect indices finite has a singular unitary dilation if and only if it is the direct sum of a singular unitary operator and aC
0(N) contraction. Such results display a scenario which is in marked contrast to that of the classical case where we have the absolute continuity of the minimal unitary power dilation of any completely nonunitary contraction. |
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Keywords: | Primary 47A20 Secondary 47A55 |
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