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Local spectral theory for normal operators in Krein spaces
Author(s) -
Philipp F.,
Strauss V.,
Trunk C.
Publication year - 2013
Publication title -
mathematische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 50
eISSN - 1522-2616
pISSN - 0025-584X
DOI - 10.1002/mana.201000141
Subject(s) - mathematics , hilbert space , operator (biology) , spectrum (functional analysis) , compact operator on hilbert space , quasinormal operator , pure mathematics , nuclear operator , mathematical analysis , compact operator , multiplication operator , finite rank operator , quantum mechanics , physics , biochemistry , chemistry , repressor , computer science , transcription factor , banach space , extension (predicate logic) , gene , programming language
Sign type spectra are an important tool in the investigation of spectral properties of selfadjoint operators in Krein spaces. It is our aim to show that also sign type spectra for normal operators in Krein spaces provide insight in the spectral nature of the operator: If the real part and the imaginary part of a normal operator in a Krein space have real spectra only and if the growth of the resolvent of the imaginary part (close to the real axis) is of finite order, then the normal operator possesses a local spectral function defined for Borel subsets of the spectrum which belong to positive (negative) type spectrum. Moreover, the restriction of the normal operator to the spectral subspace corresponding to such a Borel subset is a normal operator in some Hilbert space. In particular, if the spectrum consists entirely out of positive and negative type spectrum, then the operator is similar to a normal operator in some Hilbert space. We use this result to show the existence of operator roots of a class of quadratic operator polynomials with normal coefficients.