Weyl-Titchmarsh Theory for Sturm-Liouville Operators with Distributional Potentials

Abstract

We systematically develop Weyl-Titchmarsh theory for singular differential operators on arbitrary intervals $(a,b)\subseteq \mathbb{R}$ associated with rather general differential expressions of the type \[ τf = \frac{1}{r} (- \big(p[f' + s f]\big)' + s p[f' + s f] + qf),] where the coefficients $p$, $q$, $r$, $s$ are real-valued and Lebesgue measurable on $(a,b)$, with $p\ne 0$, $r>0$ a.e.\ on $(a,b)$, and $p^{-1}$, $q$, $r$, $s\in L_{\text{loc}}^1((a,b);dx)$, and $f$ is supposed to satisfy [f \in AC_{\text{loc}}((a,b)), \; p[f' + s f] \in AC_{\text{loc}}((a,b)).] In particular, this setup implies that $\tau$ permits a distributional potential coefficient, including potentials in $H_{\text{loc}}^{-1}((a,b))$. We study maximal and minimal Sturm-Liouville operators, all self-adjoint restrictions of the maximal operator $T_{\text{max}}$, or equivalently, all self-adjoint extensions of the minimal operator $T_{\text{min}}$, all self-adjoint boundary conditions (separated and coupled ones), and describe the resolvent of any self-adjoint extension of $T_{\text{min}}$. In addition, we characterize the principal object of this paper, the singular Weyl-Titchmarsh-Kodaira $m$-function corresponding to any self-adjoint extension with separated boundary conditions and derive the corresponding spectral transformation, including a characterization of spectral multiplicities and minimal supports of standard subsets of the spectrum. We also deal with principal solutions and characterize the Friedrichs extension of $T_{\text{min}}$. Finally, in the special case where $\tau$ is regular, we characterize the Krein-von Neumann extension of $T_{\text{min}}$ and also characterize all boundary conditions that lead to positivity preserving, equivalently, improving, resolvents (and hence semigroups).

80 pages. arXiv admin note: text overlap with arXiv:1105.3755

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Cited by in corpus (4)

• Formally self-adjoint quasi-differential operators and boundary value problems
• On Spectral Deformations and Singular Weyl Functions for One-Dimensional Dirac Operators
• On Leighton's Comparison Theorem
• Spectral gaps of the Hill--Schrödinger operators with distributional potentials