2,673 research outputs found
Perturbative HFB model for many-body pairing correlations
We develop a perturbative model to treat the off-diagonal components in the
Hartree-Fock-Bogoliubov (HFB) transformation matrix, which are neglected in the
BCS approximation. Applying the perturbative model to a weakly bound nucleus
Ni, it is shown that the perturbative approach reproduces well the
solutions of the HFB method both for the quasi-particle energies and the radial
dependence of quasi-particle wave functions. We find that the non-resonant part
of the continuum single-particle state can acquire an appreciable occupation
probability when there exists a weakly bound state close to the Fermi surface.
This result originates from the strong coupling between the continuum particle
state and the weakly bound state, and is absent in the BCS approximation. The
limitation of the BCS approximation is pointed out in comparison with the HFB
and the present perturbative model.Comment: 6 pages, 5 eps figure
Pairing correlations in nuclei on the neutron-drip line
Paring correlations in weakly bound nuclei on the edge of neutron drip line
is studied by using a three-body model. A density-dependent contact interaction
is employed to calculate the ground state of halo nuclei He and
Li, as well as a skin nucleus O. Dipole excitations in these
nuclei are also studied within the same model. We point out that the di-neutron
type correlation plays a dominant role in the halo nuclei He and
Li having the coupled spin of the two neutrons =0, while the
correlation similar to the BCS type is important in O. Contributions of
the spin =1 and S=0 configurations are separately discussed in the low
energy dipole excitations.Comment: 6 pages, 12 eps figure
Nuclear Excitations Described by Randomly Selected Multiple Slater Determinants
We propose a new stochastic method to describe low-lying excited states of
finite nuclei superposing multiple Slater determinants without assuming
generator coordinates a priori. We examine accuracy of our method by using
simple BKN interaction.Comment: Talk at International Symposium on Correlation Dynamics in Nuclei,
Tokyo, Japan, 31 Jan.-- 4 Feb. 200
Strong dineutron correlation in 8He and 18C
We study the spatial structure of four valence neutrons in the ground state
of He and C nuclei using a core+4 model. For this purpose, we
employ a density-dependent contact interaction among the valence neutrons, and
solve the five-body Hamiltonian in the Hartree-Fock-Bogoliubov (HFB)
approximation. We show that two neutrons with the coupled spin of =0 exhibit
a strong dineutron correlation around the surface of these nuclei, whereas the
correlation between the two dineutrons is much weaker. Our calculation
indicates that the probability of the (1p and [(1p
(p] configurations in the ground state wave function of He
nucleus is 34.9% and 23.7%, respectively. This is consistent with the recent
experimental finding with the He(He reaction, that is, the ground
state wave function of He deviates significantly from the pure
(1p structure.Comment: 10 pages, 9 figures, 3 table
BCS-BEC crossover of neutron pairs in symmetric and asymmetric nuclear matter
We propose new types of density dependent contact pairing interaction which
reproduce the pairing gaps in symmetric and neutron matter obtained by a
microscopic treatment based on the nucleon-nucleon interaction. These
interactions are able to simulate the pairing gaps of either the bare
interaction or the interaction screened by the medium polarization effects. It
is shown that the medium polarization effects cannot be cast into the density
power law function usually introduced together with the contact interaction and
require the introduction of another isoscalar term. The BCS-BEC crossover of
neutrons pairs in symmetric and symmetric nuclear matter is studied by using
these contact interactions. It is shown that the bare and screened pairing
interactions lead to different features of the BCS-BEC crossover in symmetric
nuclear matter. For the screened pairing interaction, a two-neutron BEC state
is formed in symmetric matter at fm (neutron density
). Contrary the bare interaction does not form the
BEC state at any neutron density
Fluctuation and dissipation dynamics in fusion reactions from stochastic mean-field approach
By projecting the stochastic mean-field dynamics on a suitable collective
path during the entrance channel of heavy-ion collisions, expressions for
transport coefficients associated with relative distance are extracted. These
transport coefficients, which have similar forms to those familiar from nucleon
exchange model, are evaluated by carrying out TDHF simulations. The
calculations provide an accurate description of the magnitude and form factor
of transport coefficients associated with one-body dissipation and fluctuation
mechanism.Comment: 9 pages, 5 figure
On the Solution of the Number-Projected Hartree-Fock-Bogoliubov Equations
The numerical solution of the recently formulated number-projected
Hartree-Fock-Bogoliubov equations is studied in an exactly soluble
cranked-deformed shell model Hamiltonian. It is found that the solution of
these number-projected equations involve similar numerical effort as that of
bare HFB. We consider that this is a significant progress in the mean-field
studies of the quantum many-body systems. The results of the projected
calculations are shown to be in almost complete agreement with the exact
solutions of the model Hamiltonian. The phase transition obtained in the HFB
theory as a function of the rotational frequency is shown to be smeared out
with the projection.Comment: RevTeX, 11 pages, 3 figures. To be published in a special edition of
Physics of Atomic Nuclei (former Sov. J. Nucl. Phys.) dedicated to the 90th
birthday of A.B. Migda
Relativistic Hartree-Bogoliubov description of ground-state properties of Ni and Sn isotopes
The Relativistic Hartree Bogoliubov (RHB) theory is applied in the
description of ground-state properties of Ni and Sn isotopes. The NL3 parameter
set is used for the effective mean-field Lagrangian, and pairing correlations
are described by the pairing part of the finite range Gogny interaction D1S.
Fully self-consistent RHB solutions are calculated for the Ni () and Sn () isotopes. Binding energies, neutron separation
energies, and proton and neutron radii are compared with experimental
data. The model predicts a reduction of the spin-orbit potential with the
increase of the number of neutrons. The resulting energy splittings between
spin-orbit partners are discussed, as well as pairing properties calculated
with the finite range effective interaction in the channel.Comment: 11 pages, RevTex, 12 p.s figures, submitted to Phys. Rev.
Quantum number projection at finite temperature via thermofield dynamics
Applying the thermo field dynamics, we reformulate exact quantum number
projection in the finite-temperature Hartree-Fock-Bogoliubov theory. Explicit
formulae are derived for the simultaneous projection of particle number and
angular momentum, in parallel to the zero-temperature case. We also propose a
practical method for the variation-after-projection calculation, by
approximating entropy without conflict with the Peierls inequality. The quantum
number projection in the finite-temperature mean-field theory will be useful to
study effects of quantum fluctuations associated with the conservation laws on
thermal properties of nuclei.Comment: 27 pages, using revtex4, to be published in PR
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