Unitary-Model-Operator Approach to Nuclear Many-Body Problem. I: --The Ground-State and One-Body Energies of 16O--

Abstract

A theory is formulated to derive an effective interaction in nuclei in the framework of the unitary­ model-operator approach. A unitary operator is introduced to describe two-body correlations, and it is determined from the condition that the effective interaction should be decoupled between the low­ momentum model space and the high-momentum space. The unitary-transformed Hamiltonian is re­ presented in a cluster expansion form. The one- and two-body cluster terms are mainly discussed. The theory is applied to the calculation of the energies of the ground- and one-body states with the Reid soft core potential. A large gain of the energy has been obtained for the ground state in comparison with the result of the usual G-matrix theory. As for the one-body energies obtained, agreement with the exper­ imental values is fairly good. Although the discrepancies with the experiments still remain at the 1O~ 15 % level, the present approach shows to have some desirable features compared with the nuclear many-body theories proposed so far.