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Borel structure of the spectrum of a closed operator

Functional Analysis 2014-11-03 v1 Spectral Theory

Abstract

For a linear operator TT in a Banach space let σp(T)\sigma_p(T) denote the point spectrum of TT, σp[n](T)\sigma_{p[n]}(T) for finite n>0n > 0 be the set of all λσp(T)\lambda \in \sigma_p(T) such that dimker(Tλ)=n\dim \ker (T - \lambda) = n and let σp[](T)\sigma_{p[\infty]}(T) be the set of all λσp(T)\lambda \in \sigma_p(T) for which ker(Tλ)\ker (T - \lambda) is infinite-dimensional. It is shown that σp(T)\sigma_p(T) is Fσ\mathcal{F}_{\sigma}, σp[](T)\sigma_{p[\infty]}(T) is Fσδ\mathcal{F}_{\sigma\delta} and for each finite nn the set σp[n](T)\sigma_{p[n]}(T) is the intersection of an Fσ\mathcal{F}_{\sigma} and a Gδ\mathcal{G}_{\delta} set provided TT is closable and the domain of TT is separable and weakly σ\sigma-compact. For closed densely defined operators in a separable Hilbert space H\mathcal{H} more detailed decomposition of the spectra is done and the algebra of all bounded linear operators on H\mathcal{H} is decomposed into Borel parts. In particular, it is shown that the set of all closed range operators on H\mathcal{H} is Borel.

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Cite

@article{arxiv.1107.1512,
  title  = {Borel structure of the spectrum of a closed operator},
  author = {Piotr Niemiec},
  journal= {arXiv preprint arXiv:1107.1512},
  year   = {2014}
}

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11 pages