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We investigate the singular Weyl–Titchmarsh m-function of perturbed spherical Schrödinger operators (also known as Bessel operators) under the assumption that the perturbation q(x) satisfies xq(x) ∈ L1(0, 1). We show existence plus detailed properties of a fundamental system of solutions which are entire with respect to the energy parameter. Based on this we show that the singular mfunction belongs to the generalized Nevanlinna class and connect our results with the theory of super singular perturbations.
Kostenko, A., Teschl, G. (2011). On The Singular Weyl-Titchmarsh Function Of Perturbed Spherical Schrödinger Operators. Journal of differential equations, 250 (2011) 3701–3739. doi:10.1016/j.jde.2010.10.026