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Boundary conditions of Sturm-Liouville operators with mixed spectra. (English) Zbl 1056.34099

The authors consider Sturm-Liouville operators on the half-line generated by the differential expression \(l(y)\equiv -y''(x)+v(x)y(x)\), \(0\leq x<\infty\), and by the boundary condition \(y(0)\cos\alpha-y'(0)\sin\alpha=0\), \(\alpha\in[0,\pi)\). Spectral properties of these operators are studied. In particular, the authors study bounds on averages of spectral functions corresponding to these operators. As a consequence, constraints are obtained which imply the existence of a singular spectrum embedded in the a.c. spectrum for sets of boundary conditions with positive measure and potentials vanishing on an interval \([0,N]\). These constraints are related to estimates on the measure of sets where the spectral density is positive.

MSC:

34L40 Particular ordinary differential operators (Dirac, one-dimensional Schrödinger, etc.)
34L05 General spectral theory of ordinary differential operators
Full Text: DOI

References:

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