L. Brito

Instabilities in asymmetric nuclear matter

The existence of phase transitions from liquid to gas phases in asymmetric nuclear matter (ANM) is related with the instability regions which are limited by the spinodals. In this work we investigate the instabilities in ANM described within relativistic mean field hadron models, both with constant and density dependent couplings at zero and finite temperatures. In calculating the proton and neutron chemical potentials we have used an expansion in terms of Bessel functions that is convenient at low densities. The role of the isovector scalar {delta}-meson is also investigated in the framework of relativistic mean field models and density dependent hadronic models. It is shown that the main differences occur at finite temperature and large isospin asymmetry close to the boundary of the instability regions.

Cluster formation in compact stars: Relativistic versus Skyrme nuclear models

We present various properties of nuclear and compact-star matter, comparing the predictions from two kinds of phenomenological approaches: relativistic models (with both constant and density-dependent couplings) and nonrelativistic Skyrme-type interactions. We mainly focus on the liquid-gas instabilities that occur at subsaturation densities, leading to the decomposition of the homogeneous matter into a clusterized phase. Such study is related to the description of neutron-star crust (at zero temperature) and supernova dynamics (at finite temperature).

Energetics of charge distributions

We consider isotropic static distributions of a given electric charge in a sphere and show that the minimal energy occurs for the uniform surface distribution, as in a charged spherical conductor in electrostatic equilibrium. Moreover, we show that the energy of such uniform distribution is minimal and stationary with respect to perturbations of the charge density, in particular dipole fluctuations. We argue that the use of the minimum energy principle to explain static distributions of electric charge provides interesting physical insights.

The q-deformed Moszkowski model: RPA modes

The behaviour of the Moszkowski model within the context of quantum algebras is studied. The Moszkowski Hamiltonian is exactly diagonalized for various values of the deformation parameter of the involved quantum algebra. The phase transition from a vibrational regime to a rotational regime is discussed in terms of the q-deformation. A coherent state for the ground state is introduced, and the Hartree-Fock energy and the RPA frequencies are compared with the exact values. The meaning of the q-deformation in this model is discussed.

Surface tension and nuclear low-lying vibrations in a fluid-dynamical approach☆

Abstract As a development of a previous variational approach to the Vlasov dynamics of small amplitude nuclear oscillations, a phenomenological surface energy is considered. This is shown to yield a finite energy to the low-lying states, while keeping unchanged the main features of the nuclear fluid.

Low-density expansion and isospin dependence of nuclear energy functional: Comparison between relativistic and Skyrme models

In the present work, we take the nonrelativistic limit of relativistic models and compare the obtained functionals with the usual Skyrme parametrization. Relativistic models with both constant couplings and with density-dependent couplings are considered. While some models already present very good results at the lowest order in the density, models with nonlinear terms only reproduce the energy functional if higher order terms are taken into account in the expansion.

Interaction between first sound and zero sound degrees of freedom

Abstract A new fluid-dynamical description of giant resonances which avoids the scaling approximation and takes into account the interplay between first sound and zero sound is presented. The new method leads to equations satisfying the sum rules S 1 and S −1 . Numerical results for the energy spectrum of 208 Pb are presented.

Light clusters in nuclear matter and the “pasta” phase

The effects of including light clusters in nuclear matter at low densities are investigated within four different parametrizations of relativistic models at finite temperature. Both homogeneous and inhomogeneous matter (pasta phase) are described for neutral nuclear matter with fixed proton fractions. We discuss the effect of the density dependence of the symmetry energy, the temperature and the proton fraction on the non-homogeneous matter forming the inner crust of proto-neutron stars. It is shown that the number of nucleons in the clusters, the cluster proton fraction and the sizes of the Wigner Seitz cell and of the cluster are very sensitive to the density dependence of the symmetry energy.

Dynamical properties of nuclear and stellar matter and the symmetry energy

The effects of density dependence of the symmetry energy on the collective modes and dynamical instabilities of cold and warm nuclear and stellar matter are studied in the framework of relativistic mean-field hadron models. The existence of the collective isovector and possibly an isoscalar collective mode above saturation density is discussed. It is shown that soft equations of state do not allow for a high-density isoscalar collective mode; however, if the symmetry energy is hard enough, an isovector mode will not disappear at high densities. The crust-core transition density and pressure are obtained as a function of temperature for {beta}-equilibrium matter with and without neutrino trapping. Estimations of the size of the clusters formed in the nonhomogeneous phase, as well as the corresponding growth rates and distillation effect, are made. It is shown that cluster sizes increase with temperature, that the distillation effect close to the inner edge of the crust-core transition is very sensitive to the symmetry energy, and that, within a dynamical instability calculation, the pasta phase exists in warm compact stars up to 10-12 MeV.

Note on the applicability of the Peierls-Yoccoz method

Abstract A simple criterion for the approximate validity of the single projection Peierls-Yoccoz method is discussed. A procedure for chosing the generator coordinate is proposed.