Collective pair excitations in dynamical nuclear field theory, 2

For the study of collective excitations in a superconducting nuclear system with the pairing force, the dynamical nuclear field theory (DNFT) is extended so as to include higher-order effects. Effective number and pair-creation operators are evaluated up to second-order in the amplitudes of the pair rotation or vibration. The number equation and the self-consistency condition are extended to the same order accordingly, while the effective Hamiltonian is calculated up to third-order. Physical interpretation of the results becomes easy if renormalized collective parameters are used. Decoupling of the pair rotation and the pair vibration is shown to persist in the higher-order approximation. (author)