Aziz Rabhi

Quark-hadron phase transition in a neutron star under strong magnetic fields

We study the effect of a strong magnetic field on the properties of neutron stars with a quark–hadron phase transition. It is shown that the magnetic field prevents the appearance of a quark phase, enhances the leptonic fraction, decreases the baryonic density extension of the mixed phase and stiffens the total equation of state, including both the stellar matter and the magnetic field contributions. Two parametrizations of a density-dependent static magnetic field, increasing, respectively, fast and slowly with the density and reaching 2–4 × 1018 G in the centre of the star, are considered. The compact stars with strong magnetic fields have maximum mass configurations with larger masses and radii and smaller quark fractions. The parametrization of the magnetic field with density has a strong influence on the star properties.

Interplay between the symmetry energy and the strangeness content of neutron stars

The effect of the density dependence of the nucleonic equation of state and the hyperon meson couplings on the star properties, including strangeness content, mass and radius, are studied within a relativistic mean field formalism. It is shown that there is still lacking information on the nucleonic equation of state at supra-saturation densities and on the hyperon interactions in nuclear matter that will allow a clear answer to the question whether the mass of the pulsar J1614-2230 could rule out exotic degrees of freedom from the interior of compact stars. We show that some star properties are affected in a similar way by the density dependence of the symmetry energy and the hyperon content of the star. To disentangle these two effects it is essential to have a good knowledge of the equation of state at supra-saturation densities. A linear correlation between the radius and the strangeness content of a star with a fixed mass is obtained.

Stellar matter with a strong magnetic field within density-dependent relativistic models

The effect of strong magnetic fields on the equation of state (EoS) for compact stars described with density-dependent relativistic hadronic models is studied. A comparison with other mean-field relativistic models is done. It is shown that the largest differences between models occur for low densities, and that the magnetic field affects the crust properties of a star, namely its extension.

Dense stellar matter with trapped neutrinos under strong magnetic fields

We investigate the effects of strong magnetic fields on the equation of state of dense stellar neutrino-free and neutrino-trapped matter. Relativistic nuclear models both with constant couplings (NLW) and with density-dependent parameters (DDRH) and including hyperons are considered. It is shown that at low densities, neutrinos are suppressed in the presence of the magnetic field. The magnetic field reduces the strangeness fraction of neutrino-free matter and increases the strangeness fraction of neutrino-trapped matter. We have studied some properties of stars with trapped neutrinos and strong magnetic fields. A density-dependent magnetic field with the magnitude 1015 G at the surface was considered. The magnetic field reduces the strangeness content of the star, and, as a consequence, the possibility of formation of a black hole after the outflow of neutrinos, since it is the appearance of exotic matter in neutrino-free matter that may induce a black-hole formation, if the EOS becomes too soft.

Imprint of the symmetry energy on the inner crust and strangeness content of neutron stars

In this work we study the effect of the symmetry energy on several properties of neutron stars. First, we discuss its effect on the density, proton fraction and pressure of the neutron star crust-core transition. We show that whereas the first two quantities present a clear correlation with the slope parameter L of the symmetry energy, no satisfactory correlation is seen between the transition pressure and L . However, a linear combination of the slope and curvature parameters at ρ = 0.1 fm−3 is well correlated with the transition pressure. In the second part we analyze the effect of the symmetry energy on the pasta phase. It is shown that the size of the pasta clusters, number of nucleons and the cluster proton fraction depend on the density dependence of the symmetry energy: a small L gives rise to larger clusters. The influence of the equation of state at subsaturation densities on the extension of the inner crust of the neutron star is also discussed. Finally, the effect of the density dependence of the symmetry energy on the strangeness content of neutron stars is studied in the last part of the work. It is found that charged (neutral) hyperons appear at smaller (larger) densities for smaller values of the slope parameter L. A linear correlation between the radius and the strangeness content of a star with a fixed mass is also found.

Magnetic susceptibility and magnetization properties of asymmetric nuclear matter in a strong magnetic field

We study the effect of a strong magnetic field on the proton and neutron spin polarization and magnetic susceptibility of asymmetric nuclear matter within a relativistic mean-field approach. It is shown that magnetic fields

Quark matter under strong magnetic fields in chiral models

B \sim 10^{16} - 10^{17}

Spinodal instabilities and the distillation effect in nuclear matter under strong magnetic fields.

G have already noticeable effects on the range of densities of interest for the study of the crust of a neutron star. Although the proton susceptibility is larger for weaker fields, the neutron susceptibility becomes of the same order or even larger for small proton fractions and subsaturation densities for

Random phase approximation for the 1D anti-ferromagnetic Heisenberg model

B > 10^{16}

Compact stars and the symmetry energy

G. We expect that neutron superfluidity in the crust will be affected by the presence of magnetic fields.