arXiv subjects

Constança Providência

Publications and source records attributed to Constança Providência.

149 records · Page 9Linked to original sources

arXiv2009

The Bonn nuclear quark model revisited

We present the exact solutions to the equations of the lowest energy states of the colored and color-symmetric sectors of the Bonn quark model, which is SU(3) symmetric and is defined in terms of an effective pairing force with $su(4)$ algebraic structure. We show that the groundstate of the model is not color symmetrical except for a narrow interval in the range of possible quark numbers. We also study the performance of the Glauber coherent state, as well as of superconducting states of the BCS type, with respect to the description, not only of the absolute (colored) groundstate, but also of the minimum energy state of the color-symmetrical sector, finding that it is remarkably good. We use the model to discuss, in a schematic context, some controversial aspects of the conventional treatment of color superconductivity.

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arXiv2009

Dynamical instabilities of warm $npe^-$ matter: the $δ$ meson effects

The effects of $δ$ 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$ρ$ and NL$ρδ$) 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 $β$-equilibrium matter with and without neutrino trapping. An estimation of the size of the clusters formed in the non-homogeneous phase is made. It is shown that cluster sizes increase with temperature. The effects of the $δ$-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 $\sim 0.4ρ_0$ and has the opposite effect below that density.

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arXiv2009

Low density instabilities in asymmetric nuclear matter within QMC with $δ$-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 QMC$δ$ models are compared with mean-field relativistic models. The distillation effect in the QMC model is discussed.

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arXiv2008

Cluster formation in compact stars: relativistic versus Skyrme models

We present various properties of nuclear and compact-star matter, comparing the predictions from two kinds of phenomenological approaches: relativistic models (both with constant and density-dependent couplings) and non-relativistic Skyrme-type interactions. We mainly focus on the liquid-gas instabilities that occur at sub-saturation 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 of supernova dynamics (at finite temperature).

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arXiv2006

Short range correlations in relativistic nuclear matter models

Short range correlations are introduced using unitary correlation method in a relativistic approach to the equation of state of the infinite nuclear matter in the framework of the Hartree-Fock approximation. It is shown that the correlations give rise to an extra node in the ground-state wave-function in the nucleons, contrary to what happens in non-relativistic calculations with a hard core. The effect of the correlations in the ground state properties of the nuclear matter and neutron matter is studied. The nucleon effective mass and equation of state (EOS) are very sensitive to short range correlations. In particular, if the pion contact term is neglected a softening of the EOS is predicted. Correlations have also an important effect on the neutron matter EOS which presents no binding but only a very shallow minimum contrary to the Walecka model.

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