Abstract

The paper contains an expanded version of my lectures in the Edinburgh school on Spectral Theory and Geometry (Spring 1998). I tried to make the exposition as selfcontained as possible.

The main object of this paper is a Schrödinger operator H = –Δ + – V(x) on a noncompact Riemannian manifold M. We discuss two basic questions of the spectral theory for such operators: conditions of the essential self-adjointness (or quantum completeness), and conditions for the discreteness of the spectrum in terms of the potential V.

In the first part of the paper we provide a shorter and a more transparent proof of a remarkable result by I. Oleinik [81, 82, 83], which implies practically all previously known results about essential self-adjointness in absence of local singularities of the potential. This result gives a sufficient condition of the essential self-adjointness of a Schrodinger operator with a locally bounded potential in terms of the completeness of the dynamics for a related classical system. The simplification of the proof given by I. Oleinik is achieved by an explicit use of the Lipschitz analysis on the Riemannian manifold and also by additional geometrization arguments which include a use of a metric which is conformal to the original one with a factor depending on the minorant of the potential.

In the second part of the paper we consider the case when the potential V is semibounded below and the manifold M has bounded geometry.