Exact solution of mean-field plus an extended T=1 nuclear pairing Hamiltonian in the seniority-zero symmetric subspace

An extended pairing Hamiltonian that describes multi-pair interactions among isospin T=1 and angular momentum J=0 neutron–neutron, proton–proton, and neutron–proton pairs in a spherical mean field, such as the spherical shell model, is proposed based on the standard T=1 pairing formalism. The advantage of the model lies in the fact that numerical solutions within the seniority-zero symmetric subspace can be obtained more easily and with less computational time than those calculated from the mean-field plus standard T=1 pairing model. Thus, large-scale calculations within the seniority-zero symmetric subspace of the model is feasible. As an example of the application, the average neutron–proton interaction in even–even N∼Z nuclei that can be suitably described in the f5pg9 shell is estimated in the present model, with a focus on the role of np-pairing correlations. Keywords: T=1 pairing interaction, Exact solution, np-pairing correlation