Spectral theory of operator measures in Hilbert space
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M. M. Malamud and S. M. Malamud
Translated by: S. V. Kislyakov - St. Petersburg Math. J. 15 (2004), 323-373
- DOI: https://doi.org/10.1090/S1061-0022-04-00812-X
- Published electronically: April 2, 2004
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Abstract:
In §2 the spaces $L^2(\Sigma ,H)$ are described; this is a solution of a problem posed by M. G. Kreĭn.
In §3 unitary dilations are used to illustrate the techniques of operator measures. In particular, a simple proof of the Naĭmark dilation theorem is presented, together with an explicit construction of a resolution of the identity. In §4, the multiplicity function $N_{\Sigma }$ is introduced for an arbitrary (nonorthogonal) operator measure in $H$. The description of $L^2(\Sigma ,H)$ is employed to show that this notion is well defined. As a supplement to the Naĭmark dilation theorem, a criterion is found for an orthogonal measure $E$ to be unitarily equivalent to the minimal (orthogonal) dilation of the measure $\Sigma$.
In §5 it is proved that the set $\Omega _{\Sigma }$ of all principal vectors of an arbitrary operator measure $\Sigma$ in $H$ is massive, i.e., it is a dense $G_{\delta }$-set in $H$. In particular, it is shown that the set of principal vectors of a selfadjoint operator is massive in any cyclic subspace.
In §6, the Hellinger types are introduced for an arbitrary operator measure; it is proved that subspaces realizing these types exist and form a massive set.
In §7, a model of a symmetric operator in the space $L^2(\Sigma ,H)$ is studied.
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Bibliographic Information
- M. M. Malamud
- Affiliation: Department of Mathematics, Donetsk National University, Universitetskaya 24, Donetsk 83055, Ukraine
- MR Author ID: 193515
- Email: mdm\@dc.donetsk.ua
- S. M. Malamud
- Affiliation: Department of Mathematics, Donetsk National University, Universitetskaya 24, Donetsk 83055, Ukraine
- Email: mdm\@dc.donetsk.ua
- Received by editor(s): June 19, 2002
- Published electronically: April 2, 2004
- © Copyright 2004 American Mathematical Society
- Journal: St. Petersburg Math. J. 15 (2004), 323-373
- MSC (2000): Primary 47B15; Secondary 47A10
- DOI: https://doi.org/10.1090/S1061-0022-04-00812-X
- MathSciNet review: 2052164