The Wiener integral and perturbation theory of the Schrödinger operator
Donald G. Babbitt
Introduction.It has been known for a long time that the Wiener integral can be effectively used in studying various properties of the Schrödinger operator A-V(x) where A = d 2 /dxl + ' ' ' +d 2 /dx 2 n , the Laplacian in m-dimensional Euclidean space E m and V(x) is a realvalued function on E m satisfying certain regularity conditions.For example, see works by Kac [6], Getoor [2; 3], Ray [9] and Nelson [8].Getoor [2] was the first to point out the connection between a Wiener type integral and the perturbation theory of certain operators of the form Q -V(x) where 0 is the infinitesimal generator of a homogeneous Markov process on a locally compact metric space X and V(x) is a real-valued Borel measurable function on X, bounded on bounded sets and bounded below everywhere.When X -E m and the Markov process is a suitably normed Wiener process, 2 12= A and his results apply to the Schrödinger operator A-V(x).In this paper we will only consider the case X = E m and Q -A but V(x) will be allowed to have certain singularities precluded by Getoor's conditions on V.For example, we can consider the perturbation of A+e/r, where X = E Z and r= (x 2 -\-y 2 +z 2 ) 112 , i.e., the Schrödinger operator with attractive Coulomb potential.In particular the essential condition on V(x) is that A -V is semi-bounded above on a certain dense domain D in L 2 (£ w ), the Hubert space of complexvalued square summable function on E m .z Main results.In this section we will introduce some notation, state our theorems and corollaries, sketch one proof and remark on the remaining proofs.Co(E m ) will denote the space of infinitely differentiable, complexvalued functions on E m with compact support.Let L l ™(E m ) denote 1 The preparation of this paper was sponsored in part by the National Science Foundation.2 In particular we assume a 2 = 2 where a 2 is the variance per unit of time of the Wiener process.See [6]. DEFINITION. A symmetric operator A with domain DÇ-L2(E m) is said to be semibounded from above if there exists a real number k< oo such that (A^, ^)^k{\p, \j/) s&||^|| 2 for all ^££> and where (</>, xl/)=f<f>^dx.
Bulletin of the American Mathematical Society•Jan 1, 1964•8 citations