Solution of The Heisenberg Equation For The Four-fermion Contact   Interaction by The Method of Dynamical Mappings
  In the paper we consider non-relativistic analog of the Nambu-Jona-Lasinio model and demonstrate, by this most simplified example, the method of dynamical mappings of Heisenberg fields on "physical" fields. We obtain the expressions for one particle eigen-excitation spectrum of full Hamiltonian (spectrum of "clad" fermions), wave function of two excitations' bound state and its mass, and compute the Bethe-Solpither amplitude. We derive as well the relation for the density of vacuum energy as a function of mapping parameters. The minimization of energy leads us to the fixation of these parameters. The method admits the generalization on the relativistic case. 
A.N.Vall, V.M.Leviant and A.V.Sinitskaya