Nonperturbative approach to a simple model with ultraviolet divergent   eigenenergies in perturbation theory
  We study a simple model for which perturbation theory gives ultravioletly divergent results. We show that when the eigen-solution problem of the Hamiltonian of the model is treated nonperturbatively, it is possible for eigenenergies of the Hamiltonian to be finite. 
Wen-ge Wang