The solution of time dependent Hartree-Fock-Bogoliubov equations by the Wigner function moments method leads to the appearance of low lying modes whose description requires the accurate knowledge of the anomalous density matrix. It is shown, that calculations with the Woods Saxon potential satisfy to this requirement.
An extension of the time-dependent Hartree-Fock-Bogoliubov theory (ETDHFB) which includes higher-order effects such as screening of the pairing correlation is proposed. ETDHFB is applied to a pairing model and a fermion system trapped in a harmonic potential to test its feasibility by comparison with exact solutions. With the use of perturbative expressions for the pairing tensor and the two-body density matrix derived from ETDHFB, the screening effect is investigated for atomic fermion systems and isotopes of tin nuclei. It is found that the screening effect on the pairing correlation is not significant.
A particle-number conserving approach is presented to solve the nuclear mean-field plus pairing Hamiltonian problem with a realistic deformed Woods-Saxon single-particle potential. The method is designed for the state-dependent monopole pairing Hamiltonian $H{\^{}}_{\mathrm{pair}}={\ensuremath{\sum}}_{\ensuremath{\alpha}\ensuremath{\beta}}{G}_{\ensuremath{\alpha}\ensuremath{\beta}}{c}_{\ensuremath{\alpha}}^{\ifmmode\dagger\else\textdagger\fi{}}{c}_{\ensuremath{\alpha}\phantom{\rule{0ex}{0ex}}\ifmmode\bar\else\textasciimacron\fi{}}^{\ifmmode\dagger\else\textdagger\fi{}}{c}_{\ensuremath{\beta}\phantom{\rule{0ex}{0ex}}\ifmmode\bar\else\textasciimacron\fi{}}{c}_{\ensuremath{\beta}}$ with an arbitrary set of matrix elements ${G}_{\ensuremath{\alpha}\ensuremath{\beta}}.$ Symmetries of the Hamiltonians on the many-body level are discussed using the language of P symmetry introduced earlier in the literature and are employed to diagonalize the problem; the only essential approximation used is a many-body (Fock-space) basis cutoff. An optimal basis construction is discussed and the stability of the final result with respect to the basis cutoff is illustrated in details. Extensions of the concept of P symmetry are introduced and their consequences for an optimal many-body basis cutoff construction are exploited. An algorithm is constructed allowing to solve the pairing problems in the many-body spaces corresponding to $p\ensuremath{\sim}40$ particles on $n\ensuremath{\sim}80$ levels and for several dozens of lowest lying states with precision $\ensuremath{\sim}$(1--2) % within seconds of the CPU time on a CRAY computer. Among applications, the presence of the low-lying seniority s=0 solutions, that are usually poorly described in terms of the standard approximations (BCS, HFB), is discussed and demonstrated to play a role in the interpretation of the spectra of rotating nuclei.