444 research outputs found
A theoretical analysis of mid-mass neutron halos. What changes going from few- to many-body systems regarding neutron halos?
The present contribution summarizes the content and slightly updates the
discussion of a recently proposed theoretical analysis of the halo phenomenon
in many-fermion systems. We focus here on applications to potential neutron
halos in mid-mass nuclei.Comment: 17 pages, 19 figures. arXiv admin note: substantial text overlap with
arXiv:nucl-th/070205
Pairing in finite nuclei from low-momentum two- and three-nucleon interactions
The present contribution reviews recent advances made toward a microscopic
understanding of superfluidity in nuclei using many-body methods based on the
BCS ansatz and low-momentum inter-nucleon interactions, themselves based on
chiral effective field theory and renormalization group techniques.Comment: 15 pages, contribution to "50 years of nuclear BCS", edited by R.A.
Broglia and V. Zelevinsk
Non-empirical pairing functional
The present contribution reports the first systematic finite-nucleus
calculations performed using the Energy Density Functional method and a
non-empirical pairing functional derived from low-momentum interactions. As a
first step, the effects of Coulomb and the three-body force are omitted while
only the bare two-nucleon interaction at lowest order is considered. To cope
with the finite-range and non-locality of the bare nuclear interaction, the 1S0
channel of Vlowk is mapped onto a convenient operator form. For the first time,
neutron-neutron and proton-proton pairing correlations generated in finite
nuclei by the direct term of the two-nucleon interaction are characterized in a
systematic manner. Eventually, such predictions are compared to those obtained
from empirical local functionals derived from density-dependent zero range
interactions. The characteristics of the latter are analyzed in view of that
comparison and a specific modification of their isovector density dependence is
suggested to accommodate Coulomb effects and the isovector trend of neutron
gaps at the same time.Comment: To be printed in the Proceedings of the International Les Houches
School on "Exotic Nuclei: New Challenges", May 7-18 2007, Les Houches,
France, 9 pages, 2 figures. Minor modification
Configuration mixing within the energy density functional formalism: pathologies and cures
Configuration mixing calculations performed in terms of the Skyrme/Gogny
Energy Density Functional (EDF) rely on extending the Single-Reference energy
functional into non-diagonal EDF kernels. The standard way to do so, based on
an analogy with the pure Hamiltonian case and the use of the generalized Wick
theorem, is responsible for the recently observed divergences and steps in
Multi-Reference calculations. We summarize here the minimal solution to this
problem recently proposed [Lacroix et al, arXiv:0809.2041] and applied with
success to particle number restoration[Bender et al, arXiv:0809.2045]. Such a
regularization method provides suitable corrections of pathologies for EDF
depending on integer powers of the density. The specific case of fractional
powers of the density[Duguet et al, arXiv:0809.2049] is also discussed.Comment: 5 pages, Proceedings of the French-Japanese Symposium, September
2008. To be published in Int. J. of Mod. Phys.
Pairing schemes for HFB calculations of nuclei
Several pairing schemes currently used to describe superfluid nuclei through
Hartree-Fock-Bogolyubov (HFB) calculations are briefly reviewed. We put a
particular emphasis on the regularization recipes used in connection with
zero-range forces and on the density dependence which usually complement their
definition. Regarding the chosen regularization process, the goal is not only
to identify the impact it may or may not have on pairing properties of nuclei
through spherical 1D HFB calculations but also to assess its tractability for
systematic axial 2D and 3D mean-field and beyond-mean-field calculations.Comment: 7 pages, 7 figures, Invited talk at the Workshop on New developments
in Nuclear Self-Consistent Mean-Field Theories, Yukawa Institute for
Theoretical Physics, Kyoto, Japan, May 30 - June 1, 2005, Yukawa Institute
for Theoretical Physics Report Series (Soryushi-ron kenkyu
Ab-initio Gorkov-Green's function calculations of open-shell nuclei
We present results from a new ab-initio method that uses the self-consistent
Gorkov Green's function theory to address truly open-shell systems. The
formalism has been recently worked out up to second order and is implemented
here in nuclei for the first time on the basis of realistic nuclear forces. We
find good convergence of the results with respect to the basis size in Ca44 and
Ni74 and discuss quantities of experimental interest including ground-state
energies, pairing gaps and particle addition/removal spectroscopy. These
results demonstrate that the Gorkov method is a valid alternative to
multireference approaches for tackling degenerate or near degenerate quantum
systems. In particular, it increases the number of mid-mass nuclei accessible
in an ab-initio fashion from a few tens to a few hundreds.Comment: 5 pages, 3 figure
Non-empirical pairing energy density functional. First order in the nuclear plus Coulomb two-body interaction
We perform systematic calculations of pairing gaps in semi-magic nuclei
across the nuclear chart using the Energy Density Functional method and a {\it
non-empirical} pairing functional derived, without further approximation, at
lowest order in the two-nucleon vacuum interaction, including the Coulomb
force. The correlated single-particle motion is accounted for by the SLy4
semi-empirical functional. Rather unexpectedly, both neutron and proton pairing
gaps thus generated are systematically close to experimental data. Such a
result further suggests that missing effects, i.e. higher partial-waves of the
NN interaction, the NNN interaction and the coupling to collective
fluctuations, provide an overall contribution that is sub-leading as for
generating pairing gaps in nuclei. We find that including the Coulomb
interaction is essential as it reduces proton pairing gaps by up to 40%.Comment: 6 pages, 1 figure, accepted for publication in EPJ
Isospin coupling in time-dependent-mean-field theories and decay of isovector excitations
We show that isospin non-diagonal terms should appear in the mean field
Hamiltonian when neutron-proton symmetry is broken. They give rise to charge
mixing in the single-particle wave-functions. We study the Time Dependent
Hartree-Fock response of a charge-exchange excitation which generates a charge
mixing in Ca isotopes. We find an enhancement of the low energy proton emission
in neutron-rich isotopes interpreted in terms of a charge oscillation below the
barrier.Comment: 4 pages, 3 figure
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