51�������

Abstract:

International audienceWe describe the most recent energy density functional derived within the quark meson coupling model. Although fit to the binding energies and charge radii of just seventy magic nuclei, the accuracy with which it reproduces nuclear properties across the entire periodic table is outstanding. As well as outlining a number of those results, we present an argument explaining why having a physically motivated model with a small number of parameters is especially desirable as one seeks to make predictions in new regions of N and Z. As an example we show the predictions for known super-heavy nuclei that were not included in the fit

Abstract:

The nuclear symmetry energy, together with the other saturation properties of symmetric nuclear matter, plays an important role in low energy nuclear structure of terrestrial systems, as well as astrophysical objects. In particular, its density dependence, both in sub- and supra-saturation regions in high density matter in neutron stars, is of utmost significance and has been a subject of active research for decades, usually within a mean-field framework. We report results obtained using the latest version of Quark-Meson-Coupling Model (QMC-A) with just three variable parameters, the baryon-meson coupling constants in free space. It is shown that these parameters can be determined directly using nuclear matter (NM) properties at saturation; two parameters of symmetric nuclear matter (SNM), the baryon number density and the energy per particle, and the symmetry energy coefficient of asymmetric nuclear matter (ANM). The effects of uncertainties in the these parameters and propagation of these uncertainties through the calculation of properties of dense hyperonic matter and cold neutron stars are demonstrated. This approach leads to new limits on both the NM parameters and the QMC coupling constants. The results, which exploit the unique features of the QMC model, are discussed and future prospects are outlined.

Abstract:

We systematically explore the relative impact of the Coulomb interaction and the nuclear symmetry energy on the proton and neutron density distributions in the 212Pb + 208Pb, 132Sn + 124Sn and 54Ca + 48Ca central collisions at beam energies below 800 MeV/A. The Boltzmann-Uhlenbeck-Uehling (pBUU) transport and the Time-Dependent-Hartree-Fock (TDHF) frameworks with SV-bas and SV-sym34 Skyrme parametrizations are employed. Maximum total particle number density and the proton-neutron (isospin) asymmetry have been calculated as a function of beam energy, system size and the Skyrme model, with and without the Coulomb force for all systems. The maximum total density, overall not exceeding 2.5-3.0ρ0 (ρ0=0.16fm−3), is observed to be lowered by the Coulomb interaction by less than 10%. The maximal asymmetries are not enhanced but decreased in the reaction as compared to the initial state in the majority of cases, and lowered by up to 45% due to the Coulomb effects. Furthermore, the proton and neutron density distributions in the plane transverse to the beam direction have been modelled. The distributions are found to vary throughout the reaction space, with the Coulomb force increasing the isospin differences closer to the center of the collision. The general conclusion of this work is that the Coulomb interaction plays a significant role in the collision dynamics, and enhances the rather weak response of the colliding systems to the nuclear symmetry energy and its density dependence. Thus, inferring symmetry energy from comparing theory and data requires careful modelling of Coulomb effects, in addition to nuclear, in any reaction simulation.

Abstract:

We conduct a comprehensive survey of the shape parameter space of the nuclear pasta phases in neutron star crusts by conducting three-dimensional Hartree-Fock+BCS calculations. Spaghetti, waffles, lasagna, bicontinuous phases and cylindrical holes occupy local minima in the resulting constant-pressure Gibbs energy surfaces, implying multiple geometries coexist at a given depth. Notably, the bicontinuous phase, in which both the neutron gas and nuclear matter extend continuously in all dimensions appears over a large depth range. Our results support the idea that nuclear pasta is a glassy system. At a characteristic temperature, of order 108-109K, different phases may become frozen into domains whose sizes we estimate to be 1-50 times the lattice spacing and over which the local density and electron fraction can vary. Above this temperature, very little long-range order exists and matter is an amorphous solid. Electron scattering off domain boundaries may contribute to the disorder resistivity of the pasta phases. Annealing of the domains may occur during cooling; repopulating of local minima during crustal heating might lead to temperature-dependent transport properties in the deep crust layers. We identify four regions distinguished by whether pasta is the true ground state, and whether the pasta structure allows delocalization of protons. The whole pasta region can occupy up to 70% of the crust by mass and 25% by thickness, and the layer in which protons are delocalized could occupy 45% of the crust mass and 15% of its thickness.