On Schoedinger operators with multipolar inverse-square potentials
  Positivity, essential self-adjointness, and spectral properties of a class of Schroedinger operators with multipolar inverse-square potentials are discussed. In particular a necessary and sufficient condition on the masses of singularities for the existence of at least a configuration of poles ensuring the positivity of the associated quadratic form is established. 
Veronica Felli, Elsa M. Marchini, and Susanna Terracini