Solvable mean-field plus extended pairing model

A mean-field Hamiltonian with an extended pairing interaction that includes multipair excitations is proposed for describing strongly-deformed nuclei. Solutions are easily obtained. The results show that even though the theory includes many-body interaction terms, the one- and two-body parts continue to dominate the dynamics for small values of the pairing strength. As the strength of the pairing interaction grows, however, the higher many-body interaction terms grow in importance. A numerical study of binding energies for the Yb154-181 isotopes demonstrates the applicability of the theory.