Alexander Sakhnovich

  1. Weyl-Titchmarsh Theory for Schroedinger Operators with Strongly Singular Potentials.

    Authors: Aleksey Kostenko, Alexander Sakhnovich, Gerald Teschl
    Subjects: Spectral Theory
    Abstract

    We develop Weyl-Titchmarsh theory for Schroedinger operators with strongly
    singular potentials such as perturbed spherical Schroedinger operators (also
    known as Bessel operators). It is known that in such situations one can still
    define a corresponding singular Weyl m-function and it was recently shown that
    there is also an associated spectral transformation. Here we will give a
    general criterion when the singular Weyl function can be analytically extended
    to the upper half plane.

  2. Construction of the solution of the inverse spectral problem for a system depending rationally on the spectral parameter, Borg-Marchenko-type theorem, and sine-Gordon equation.

    Authors: Alexander Sakhnovich
    Subjects: Classical Analysis and ODEs
    Abstract

    Weyl theory for a non-classical system depending rationally on the spectral
    parameter is treated. Borg-Marchenko-type uniqueness theorem is proved. The
    solution of the inverse problem is constructed. An application to sine-Gordon
    equation in laboratory coordinates is given.

  3. On the GBDT version of the B\"acklund-Darboux transformation and its applications to the linear and nonlinear equations and Weyl theory.

    Authors: Alexander Sakhnovich
    Subjects: Classical Analysis and ODEs
    Abstract

    A general theorem on the GBDT version of the B\"acklund-Darboux
    transformation for systems rationally depending on the spectral parameter is
    treated and its applications to nonlinear equations are given. Explicit
    solutions of direct and inverse problems for Dirac-type systems, including
    systems with singularities, and for the system auxiliary to the $N$-wave
    equation are reviewed. New results on explicit construction of the wave
    functions for radial Dirac equation are obtained.

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