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