turkmath.org

Generalized indefinite strings provide a canonical model for Generalized indefinite strings provide a canonical model for self-adjoint operators with simple spectrum (other classical models are Jacobi matrices, Krein strings and 2×2 canonical systems). We’ll present several Szegő-type theorems for generalized indefinite strings and related spectral problems (including Krein strings and Dirac operators). More specifically, for several classes of coefficients (that can be regarded as Hilbert–Schmidt perturbations of model problems), we provide a complete characterization of the corresponding set of spectral measures. In particular, our results also apply to the isospectral Lax operator for the conservative Camassa–Holm flow and allow us to establish existence of global weak solutions with various step-like initial conditions of low regularity via the inverse spectral transform.
The talk is based on joint work with J.Eckhardt.