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Nguyen Dinh Dang

Publications and source records attributed to Nguyen Dinh Dang.

22 records · Page 2Linked to original sources
arXiv2003

Reply by N. Dinh Dang to the Comment by A. Rabhi

It is pointed out that the ``exact'' solutions given in the recent Comment by A. Rabhi on the paper [N. Dinh Dang ``Energies of the ground state and first excited $0^{+}$ state in an exactly solvable pairing model'', Eur. Phys. Jour. A 16 (2003) 18] do not correspond to the standard exact solution of the well-known two-level pairing model. Other issues raised in the Comment reiterate the discussions already published in the original paper by N. Dinh Dang.

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arXiv2003

Modified Hartree-Fock-Bogoliubov at finite temperature

The modified HFB (MHFB) theory at finite temperature is derived, which conserves the unitarity relation of the particle-density matrix. This is achieved by constructing a modified quasiparticle-density matrix, where the fluctuation of the quasiparticle number is microscopically built in. This matrix can be directly obtained from the usual quasiparticle-density matrix by applying the secondary Bogoliubov transformation, which includes the quasiparticle occupation number. It is shown that, in the limit of constant pairing parameter, the MHFB theory yields the previously obtained modified BCS (MBCS) equations. It is also proved that the modified quasiparticle RPA, which is based on the MBCS quasiparticle excitations, conserves the Ikeda sum rule. The numerical calculations of the pairing gap, heat capacity, level density, and level density parameter within the MBCS theory are carried out for $^{120}$Sn. The results show that the superfluid - normal phase transition is completely washed out. The applicability of the MBCS up to a temperature as high as $T\sim$ 5 MeV is analyzed in detail.

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arXiv2002

Energies of the ground state and first excited $0^{+}$ state in an exactly solvable pairing model

Several approximations are tested by calculating the ground-state energy and the energy of the first excited $0^{+}$ state using an exactly solvable model with two symmetric levels interacting via a pairing force. They are the BCS approximation (BCS), Lipkin - Nogami (LN) method, random-phase approximation (RPA), quasiparticle RPA (QRPA), the renormalized RPA (RRPA), and renormalized QRPA (RQRPA). It is shown that, in the strong-coupling regime, the QRPA which neglects the scattering term of the model Hamiltonian offers the best fit to the exact solutions. A recipe is proposed using the RRPA and RQRPA in combination with the pairing gap given by the LN method. Applying this recipe, it is shown that the normal-superfluid phase transition is avoided, and a reasonably good description for both of the ground-state energy and the energy of the first excited $0^{+}$ state is achieved.

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