Discreteness of spectrum and positivity criteria for Schrödinger operators

Abstract

We provide a class of necessary and sufficient conditions for the discreteness of spectrum of Schrödinger operators with scalar potentials which are semibounded below. The classical discreteness of spectrum criterion by A. M. Molchanov (1953) uses a notion of negligible set in a cube as a set whose Wiener capacity is less than a small constant times the capacity of the cube. We prove that this constant can be taken arbitrarily between 0 and 1. This solves a problem formulated by I. M. Gelfand in 1953. Moreover, we extend the notion of negligibility by allowing the constant to depend on the size of the cube. We give a complete description of all negligibility conditions of this kind. The a priori equivalence of our conditions involving different negligibility classes is a nontrivial property of the capacity. We also establish similar strict positivity criteria for the Schrödinger operators with nonnegative potential

Authors

Vladimir Maz'ya

Department of Mathematics
The Ohio State University
Columbus, OH 43210
United States

Mikhail Shubin

Department of Mathematics
Northeastern University
Boston, MA 02115
United States