文摘
For a general subcritical second-order elliptic operator P in a domain (or noncompact manifold), we construct Hardy-weight W which is optimal in the following sense. The operator is subcritical in 惟 for all , null-critical in 惟 for , and supercritical near any neighborhood of infinity in 惟 for any . Moreover, if P is symmetric and , then the spectrum and the essential spectrum of are equal to , and the corresponding Agmon metric is complete. Our method is based on the theory of positive solutions and applies to both symmetric and nonsymmetric operators. The constructed Hardy-weight is given by an explicit simple formula involving two distinct positive solutions of the equation , the existence of which depends on the subcriticality of P in 惟.