A. M. Santos

Low density instabilities in asymmetric nuclear matter within the quark-meson coupling (QMC) model with the δ meson

In the present work we include the isovector-scalar δ-meson in the quark-meson coupling model (QMC) and study the properties of asymmetric nuclear within QMC without and with the δ-meson. Recent constraints set by isospin diffusion on the slope parameter of the nuclear symmetry energy at saturation density are used to adjust the model parameters. The thermodynamical spinodal surfaces are obtained and the instability region at subsaturation densities within QMC and QMCδ models are compared with mean-field relativistic models. The distillation effect in the QMC model is discussed.

Compact stars within a soft symmetry energy quark-meson-coupling model

We investigate compact star properties within the quark meson coupling model (QMC) with a soft symmetry energy density dependence at large densities. In particular, the hyperon content and the mass/radius curves for the families of stars obtained within the model are discussed. The hyperon-meson couplings are chosen according to experimental values of the hyperon nuclear matter potentials, and possible uncertainties are considered. It is shown that a softer symmetry energy gives rise to stars with less hyperons, smaller radii and larger masses. Hyperon-meson couplings may also have a strong effect on the mass of the star.

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.

Dynamical instabilities of warm npe- matter: The delta meson effects

The effects of {delta} mesons on the dynamical instabilities of cold and warm nuclear and stellar matter at subsaturation densities are studied in the framework of relativistic mean-field hadron models (NL3, NL{rho}, and NL{rho}{delta}) with the inclusion of the electromagnetic field. The distillation effect and the spinodals for all the models considered are discussed. The crust-core transition density and pressure are obtained as a function of temperature for {beta}-equilibrium matter with and without neutrino trapping. An estimation of the size of the clusters formed in the nonhomogeneous phase and the corresponding growth rates are made. It is shown that cluster sizes increase with temperature. The effects of the {delta} meson on the instability region are larger for low temperatures, very asymmetric matter, and densities close to the spinodal surface. It increases the distillation effect above {approx}0.4{rho}{sub 0} and has the opposite effect below that density.

Dynamical instabilities in density-dependent hadronic relativistic models

Unstable modes in asymmetric nuclear matter (ANM) at subsaturation densities are studied in the framework of relativistic mean-field density-dependent hadron models. The size of the instabilities that drive the system are calculated and a comparison with results obtained within the nonlinear Walecka model is presented. The distillation and antidistillation effects are discussed.

Nuclear pasta phases within the quark-meson coupling model

In this work the low density regions of nuclear and neutron star matter are studied. The search for the existence of pasta phases in this region is performed within the context of the quark-meson coupling (QMC) model, which incorporates quark degrees of freedom. Fixed proton fractions are considered, as well as nuclear matter in beta equilibrium at zero temperature. We discuss the recent attempts to better understand the surface energy in the coexistence phases regime and we present results that show the existence of the pasta phases subject to some choices of the surface energy coefficient. We also analyze the influence of the nuclear pasta on some neutron star properties. The equation of state containing the pasta phase will be part of a complete grid for future use in supernova simulations.

Isospin constraints on the parametric coupling model for nuclear matter

We make use of isospin constraints to study the parametric coupling model and the properties of asymmetric nuclear matter. Besides the usual constraints for nuclear matter\char22{}the effective nucleon mass and the incompressibility at saturation density\char22{}and the neutron star constraints\char22{}maximum mass and radius\char22{}we study the properties related to the symmetry energy. These properties constrain the parameters of the model to a small range. We apply our results to study thermodynamic instabilities in the liquid-gas phase transition as well as neutron star configurations.

Warm nuclear and neutron star matter and the pasta phase

The possibility of exotic structures, i. e., the “pasta” phase to be formed in the low density region of nuclear and stellar matter is investigated. The effects of the presence of α‐particles are considered in the context of relativistic nuclear models.

Dynamical Instabilities in Relativistic Mean-Field Models and Inner Edge of the Compact Star Crust

We take a dynamical spinodal approach to study the effects of different nuclear relativistic models on the instability zone of nuclear matter in β equilibrium under the conditions expected to be found in the crust of neutron stars. In particular, we probe the predictive power of those models in the description of the inner edge of the crust. Pressure and the liquid‐gas phase densities are evaluated and compared to the most recent “pasta” phase results obtained with a Thomas‐Fermi approach for the pasta phases. The collective response from n, p matter is also briefly commented.

Dynamical instabilities of warm n pe matter: the δ meson effects

The effects of the δ meson on the dynamical instabilities of cold and warm nuclear and stellar matter at subsaturation densities are studied in the framework of relativistic mean‐field hadron models (NL3, NLρ and NLρδ) with the inclusion of the electromagnetic field. The crust‐core transition density and pressure are obtained as a function of temperature of β‐equilibrium matter with and without neutrino trapping. The distillation effect is discussed. For β‐equilibrium matter with trapped neutrinos the pasta phase disappears for T>13.2 MeV (NLρ and NLρδ) or T>11.6 MeV (NL3). For neutrino free matter the non‐homogeneous phase does not exist for T>3 MeV. The δ meson has a larger effect in neutron rich matter, larger densities and smaller temperatures. It reduces the extension of the spinodal. The distillation effect is stronger for larger densities and smaller temperatures. The δ meson increases the distillation effect, for larger densities. NL3 predicts larger clusters compared with the other two parametriz...