Weyl-Titchmarsh theory

E. Brandas, M. Rittby, N. Elander, Titchmarsh-Weyl Theory and Its Relations to Scattering Theory Spectral Densities and Cross Sections Theory and Applications, J. Math. Phys. 26 (1985) 2648. 

M. Rittby, N. Elander, E. Brandas, Scattering in View of the Titchmarsh-Weyl Theory, Int. J. Quant. Chem. XXIII (1983) 865. 

In this addendum, we will derive the spectral function from Weyl s theory and in particular demonstrate the relationship between the imaginary part of the Weyl-Titchmarsh m-function, mi, and the concept of spectral concentration. For simplicity we will restrict the discussion to the spherical symmetric case with the radial coordinate defined on the real half-line. Remember that m could be defined via the Sturm-Liouville problem on the radial interval [0,b] (if zero is a singular point, the interval [a,b], b > a > 0), and the boundary condition at the left boundary is given by [commensurate with Eq. (5)]... 

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