163 research outputs found
QCD Scales and Chiral Symmetry in Finite Nuclei
We report on our progress in the calculation of nuclear ground-state
properties using effective Lagrangians whose construction is constrained by QCD
scales and chiral symmetry. Good evidence is found that QCD and chiral symmetry
apply to finite nuclei.Comment: Presentation at the International Conference on Nuclear Data for
Science and Technology, Trieste, Italy, May 19-24, 1997. LaTeX file (7 pages,
4 tables). To be published in the Conference Series of the Italian Physical
Societ
A nucleonic NJL model for finite nuclei: dynamic mass generation and ground-state observables
We test the compatibility of chiral symmetry, dynamic mass generation of the
nucleon due to spontaneous breaking of chiral symmetry, and the description of
finite nuclear systems by employing an NJL model understood as a chiral
invariant effective theory for nucleons. We apply the model to nuclear matter
as well as to finite nuclei. In the latter case, the model is adjusted to
nuclear ground-state observables. We treat the case of a pure chiral theory and
the physically more realistic case where a portion of the nucleon mass (160
MeV) explicitly breaks chiral symmetry. The best version of this current model
is found to deliver reasonably good results simultaneously for both finite
nuclei and the nucleon mass, which supports our motivation of probing a link
between low-momentum QCD and the nuclear many-body problem. However, the
observables calculated for finite nuclei are not as good as those coming from
existing relativistic mean field models without explicit chiral symmetry.Comment: 19 pages, 3 eps figures, accepted for publication in Nucl. Phys.
Recent progress in the study of fission barriers in covariant density functional theory
Recent progress in the study of fission barriers of actinides and superheavy
nuclei within covariant density functional theory is overviewed.Comment: 10 pages, 5 figures. In press in International Journal of Modern
Physics
Final excitation energy of fission fragments
We study how the excitation energy of the fully accelerated fission fragments
is built up. It is stressed that only the intrinsic excitation energy available
before scission can be exchanged between the fission fragments to achieve
thermal equilibrium. This is in contradiction with most models used to
calculate prompt neutron emission where it is assumed that the total excitation
energy of the final fragments is shared between the fragments by the condition
of equal temperatures. We also study the intrinsic excitation-energy partition
according to a level density description with a transition from a
constant-temperature regime to a Fermi-gas regime. Complete or partial
excitation-energy sorting is found at energies well above the transition
energy.Comment: 8 pages, 3 figure
On the Isovector Channels in Relativistic Point Coupling Models within the Hartree and Hartree-Fock Approximations
We investigate the consequences of Fierz transformations acting upon the
contact interactions for nucleon fields occurring in relativistic point
coupling models in Hartree approximation, which yield the same models but in
Hartree-Fock approximation instead. We find for four-fermion interactions
occurring in two existing relativistic point coupling phenomenologies that
whereas in Hartree the isovector-scalar strength, corresponding to delta-meson
exchange, is unnaturally small, indicating a possible new symmetry, in
Hartree-Fock it is instead comparable to the isovector-vector strength
corresponding to rho-meson exchange, but the sum of the two isovector coupling
constants appears to be preserved in both approaches. Furthermore, in
Hartree-Fock approximation, both QCD-scaled isovector coupling constants are
natural (dimensionless and of order 1) whereas in Hartree approximation only
that of the isovector-vector channel is natural. This indicates that it is not
necessary to search for a new symmetry and, moreover, that the role of the
delta-meson should be reexamined.Comment: 10 pages; accepted for publication in Nuclear Physics
Adjustment studies in self-consistent relativistic mean-field models
We investigate the influence of the adjustment procedure and the set of
measured observables on the properties and predictive power of relativistic
self-consistent mean-field models for the nuclear ground state. These studies
are performed with the point-coupling variant of the relativistic mean-field
model. We recommend optimal adjustment algorithms for the general two-part
problem and we identify various trends and dependencies as well as deficiencies
of current models. Consequences for model improvements are presented.Comment: 18 pages, 6 figures, revised version, accepted for publication in
Nuclear Physics
Predicting total reaction cross sections for nucleon-nucleus scattering
Nucleon total reaction and neutron total cross sections to 300 MeV for 12C
and 208Pb, and for 65 MeV spanning the mass range, are predicted using
coordinate space optical potentials formed by full folding of effective
nucleon-nucleon interactions with realistic nuclear ground state densities.
Good to excellent agreement is found with existing data.Comment: 10 pages, 4 figure
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