SPECTRAL DECOMPOSITIONS OF SELF-ADJOINT OPERATORS IN PONTRYAGIN AND KREIN SPACES
摘要
We consider a self-adjoint operator acting in a Krein space and possessing an invariant subspace that is maximal nonnegative and is decomposed into a direct sum of a uniformly positive (i.e., equivalent to a Hilbert space with respect to the inner pseudoscalar product) and a finite-dimensional neutral subspace. We prove the existence of a difference expression that transforms the moment sequence generated by this operator into a sequence representable as a difference of positive moment sequences. In the case of a cyclic operator, we apply this result to construct a function space in which the operator under study is modelled as an operator of multiplication by an independent variable.