Nuclear structure and the nucleon effective mass: explorations with the versatile KIDS functional

The connection from the structure and dynamics of atomic nuclei (finite nuclear system) to the nuclear equation of state (thermodynamic limit) is primarily made through nuclear energy-density functional (EDF) theory. Failure to describe both entities simultaneously within existing EDF frameworks means that we have either seriously misjudged the scope of EDF or not fully taken advantage of it. Enter the versatile KIDS Ansatz, which is based on controlled, order-by-order extensions of the nuclear EDF with respect to the Fermi momentum and allows a direct mapping from a given, immutable equation of state to a convenient Skyrme pseudopotential for applications in finite nuclei. A recent proof-of-principle study of nuclear ground-states revealed the subversive role of the effective mass. Here we summarize the formalism and previous results and present further explorations related to giant resonances. As examples we consider the electric dipole polarizability of 68Ni and the giant monopole resonance (GMR) of heavy nuclei, particularly the fluffiness of 120Sn. We find that the choice of the effective mass parameters and that of the compression modulus affect the centroid energy of the GMR to comparable degrees.

Analysis of the flow systematics in Au+Au collisions

The new implementation of the Boltzmann-Uhling-Uhlenbeck equation, the VdWBUU simulation (with EoS-dependent in-medium nucleon-nucleon cross sections) appears to reproduce the flow observables in the Au+Au collisions in the energy range from 400 AMeV to 10 AGeV. The range of the feasible stiffness of the EoS can be identified, based on the analysis presented here, as encompassing compressibilities starting from 250-260 MeV and above, and thus consistent with the results of re-analysis of the giant monopole resonance data (250-310 MeV). Using that additional constraint, the range of feasible values of the stiffness of density dependence can be set as γ=1−1.25, with the value γ=1 appearing as as a global value of stiffness of the symmetry energy feasible over the whole range of constrained compressibilities. The implementation of BUU with the free nucleon-nucleon cross sections can not describe correctly the global trends of flow observables.

Softness of Sn isotopes in relativistic semiclassical approximation

Within the framework of relativistic Thomas–Fermi (RTF) and relativistic extended Thomas–Fermi (RETF) approximations, we calculate the giant monopole resonance (GMR) excitation energies for Sn and related nuclei. A large number of nonlinear relativistic force parameters are used in these calculations. We find a parameter set is capable to reproduce the experimental monopole energy of Sn isotopes, when its nuclear matter compressibility lies within 210–230 MeV, however, it fails to reproduce the GMR energy of other nuclei. That means, simultaneously a parameter set cannot reproduce the GMR values of Sn and other nuclei.