Shnol-type theorem for the Agmon ground state

Abstract

Let $H$ be a Schrödinger operator defined on a noncompact Riemannian manifold $\Omega$, and let $W\in L^{\infty }(\Omega ;\mathbb{R})$. Suppose that the operator $H+W$ is critical in $\Omega$, and let $\phi$ be the corresponding Agmon ground state. We prove that if $u$ is a generalized eigenfunction of $H$ satisfying $|u|\le \phi$ in $\Omega$, then the corresponding eigenvalue is in the spectrum of $H$. The conclusion also holds true if for some $K⋐\Omega$ the operator $H$ admits a positive solution in $\tilde{\Omega }=\Omega \setminus K$, and $|u|\le \psi$ in $\tilde{\Omega }$, where $\psi$ is a positive solution of minimal growth in a neighborhood of infinity in $\Omega$. Under natural assumptions, this result holds true also in the context of infinite graphs, and Dirichlet forms.