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Off-diagonal terms in symmetric operators
Journal article   Peer reviewed

Off-diagonal terms in symmetric operators

Journal of mathematical physics, Vol.41(4), pp.2337-2349
04/2000
DOI: 10.1063/1.533242
url
https://arxiv.org/pdf/math-ph/9911017View
Open Access

Abstract

In this paper we provide a quantitative comparison of two obstructions for a given symmetric operator S with dense domain in Hilbert space H to be self-adjoint. The first one is the pair of deficiency spaces of von Neumann, and the second one is of more recent vintage; Let P be a projection in H. We say that it is smooth relative to S if its range is contained in the domain of S. We say that smooth projections {P i } i=1 ∞ diagonalize S if (a) (I−P i )SP i =0 for all i, and (b) sup i  P i =I. If such projections exist, then S has a self-adjoint closure (i.e., S̄ has a spectral resolution), and so our second obstruction to self-adjointness is defined from smooth projections P i with (I−P i )SP i ≠0. We prove results both in the case of a single operator S and a system of operators.

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