Small perturbation of selfadjoint and unitary operators in Krein spaces

We investigate the behaviour of the spectrum of selfadjoint operators in Krein spaces under perturbations with uniformly dissipative operators. Moreover we consider the closely related problem of the perturbation of unitary operators with uniformly bi-expansive. The obtained perturbation results give a new characterization of spectral points of positive type and of type pi + of selfadjoint (resp. unitary) operators in Krein spaces.


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