Pairing - correlations and particle - number projection methods

A systematic study of the pairing-correlations derived from various particle-number projection methods is performed in an exactly soluble cranked-deformed shell model Hamiltonian. It is shown that most of the approximate particle-number projection methods including the method of Lipkin-Nogami, which is used quite extensively in nuclear structure studies, breakdown in the weak pairing limit. The results obtained from the recently formulated number-projected Hartree-Fock-Bogoliubov (PHFB) equations, on the other hand, are in complete agreement with the exact solutions of the model Hamil-tonian. The pairing-energy calculated from PHFB method is shown to be finite in all the studied limits. More importantly, the numerical work involved in the solution of the PHFB equations appears to be comparable to the solution of the bare HFB equations.