Weil-Titchmarsh theory as applied to the singular non-sectorial Schr\"odinger operator. Conditions for discreteness of the spectrum and compactness of the resolvent

Abstract

The spectral properties of the singular Schr\"odinger operator with complex-valued potential which takes values in a wider region than the half-plane, have been little studied. In general case, the operator is non-sectorial, and the numerical range coincides with the entire complex plane. In this situation we propose sufficient conditions for discreteness of the spectrum and compactness of the resolvent.