3-BODY SCATTERING-THEORY OF CORRELATED HOLE AND ELECTRON-STATES

We describe a theoretical scheme for the determination of quasiparticl e spectra starting from the energy band structure of a metal and treat ing the on-site Hubbard repulsion beyond the mean-field theory. The me thod relies upon an expansion of the many-body states in terms of unco rrelated states with a different number of electron-hole pairs. By tru ncating the expansion to include configurations with one or two pairs one can achieve approximate expressions of the electron and hole self- energies. The interparticle scattering matrices appearing in such expr essions are conveniently calculated using the Fadeev approach. Calcula tions performed for a constant density of states allow us to illustrat e the role of three-body correlations in the metal-insulator transitio ns.