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A. Rabhi

Publications and source records attributed to A. Rabhi.

13 recordsLinked to original sources
arXiv2015

Magnetic susceptibility and magnetization properties of asymmetric nuclear matter under 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 $B \sim 10^{16} - 10^{17}$ 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 $B > 10^{16}$ G. We expect that neutron superfluidity in the crust will be affected by the presence of magnetic fields.

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arXiv2011

Warm and dense stellar matter under strong magnetic fields

We investigate the effects of strong magnetic fields on the equation of state of warm stellar matter as it may occur in a protoneutron star. Both neutrino free and neutrino trapped matter at a fixed entropy per baryon are analyzed. A relativistic mean field nuclear model, including the possibility of hyperon formation, is considered. A density dependent magnetic field with the magnitude $10^{15}$ G at the surface and not more than $3\times 10^{18}$ G at the center is considered. The magnetic field gives rise to a neutrino suppression, mainly at low densities, in matter with trapped neutrinos. It is shown that an hybrid protoneutron star will not evolve to a low mass blackhole if the magnetic field is strong enough and the magnetic field does not decay. However, the decay of the magnetic field after cooling may give rise to the formation of a low mass blackhole.

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arXiv2011

Landau parameters for asymmetric nuclear matter with a strong magnetic field

The Landau Fermi Liquid parameters are calculated for charge neutral asymmetric nuclear matter in beta equilibrium at zero temperature in the presence of a very strong magnetic field with relativistic mean-field models. Due to the isospin structure of the system, with different populations of protons and neutrons and spin alignment to the field, we find non-vanishing Landau mixing parameters. The existence of quantized Landau levels for the charged sector has some impact on the Landau parameters with the presence of discretized features in those involving the proton sector. Using the Fermi liquid formalism singlet and triplet excited quasiparticle states are analyzed, and we find that in-medium effects and magnetic fields are competing, however, the former are more important in the interaction energy range considered. It is found that for magnetic field strengths Log$_{10}$ B (G) $\le 17$ the relative low polarization of the system produces mild changes in the generalized Landau parameters with respect to the unmagnetized case, while for larger strengths there is a resolution of the degeneracy of the interaction energies of quasiparticles in the system.

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arXiv2009

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 parametrisations of a density dependent static magnetic field, increasing, respectively, fast and slowly with the density and reaching $2-4\times 10^{18}$G in the center of the star, are considered. The compact stars with strong magnetic fields have maximum mass configurations with larger masses and radius and smaller quark fractions. The parametrisation of the magnetic field with density has a strong influence on the star properties.

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arXiv2009

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. The mass-radius relation of stars described by these equations of state are determined. The magnetic field makes the overall equation of state stiffer and the stronger the field the larger the mass of maximum mass star and the smaller the baryon density at the center of the star. As a consequence in the presence of strong magnetic fields the possibility that a protoneutron star evolves to a blackhole is smaller.

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arXiv2009

Effect of the $δ$-meson on the instabilities of nuclear matter under strong magnetic fields

We study the influence of the isovector-scalar meson on the spinodal instabilities and the distillation effect in asymmetric non-homogenous nuclear matter under strong magnetic fields, of the order of $10^{18}-10^{19}$ G. Relativistic nuclear models both with constant couplings (NLW) and with density dependent parameters (DDRH) are considered. A strong magnetic field can have large effects on the instability regions giving rise to bands of instability and wider unstable regions. It is shown that for neutron rich matter the inclusion of the $δ$ meson increases the size of the instability region for NLW models and decreases it for the DDRH models. The effect of the $δ$ meson on the transition density to homogeneous $β$-equilibrium matter is discussed. The DDRH$δ$ model predicts the smallest transition pressures, about half the values obtained for NL$δ$.

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arXiv2008

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

We study the effect of strong magnetic fields, of the order of $10^{18}$-$10^{19}$ G, on the instability region of nuclear matter at subsaturation densities. Relativistic nuclear models both with constant couplings and with density dependent parameters are considered. It is shown that a strong magnetic field can have large effects on the instability regions giving rise to bands of instability and wider unstable regions. As a consequence we predict larger transition densities at the inner edge of the crust of compact stars with strong magnetic field. The direction of instability gives rise to a very strong distillation effect if the last Landau level is only partially filled. However, for almost completed Landau levels an anti-distillation effect may occur.

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arXiv2008

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.

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arXiv2007

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

The Hartree-Fock-RPA approach is applied to the 1D anti-ferromagnetic Heisenberg model in the Jordan-Wigner representation. Somewhat contrary to expectation, this leads to reasonable results for spectral functions and sum rules in the symmetry unbroken phase. In a preliminary application of Self-Consistent RPA to finite size chains strongly improved results are obtained.

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arXiv2003

Self-consistent random phase approximation in the Schutte-Da-Providencia fermion-boson model

Self-consistent random phase approximation (SCRPA) is applied to the exactly solvable model with fermion boson coupling proposed by Schütte and Da-Providencia. Very encouraging results in comparison with the exact solution of the model for various observables are obtained. The transition from the normal phase to the phase with a spontaneously broken symmetry is carefully investigated. The strong reduction of the variance in SCRPA vs HF is pointed out.

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arXiv2002

Self-Consistent Quasi-Particle RPA for the Description of Superfluid Fermi Systems

Self-Consistent Quasi-Particle RPA (SCQRPA) is for the first time applied to a more level pairing case. Various filling situations and values for the coupling constant are considered. Very encouraging results in comparison with the exact solution of the model are obtained. The nature of the low lying mode in SCQRPA is identified. The strong reduction of the number fluctuation in SCQRPA vs BCS is pointed out. The transition from superfluidity to the normal fluid case is carefully investigated.

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arXiv2001

Restoration of broken symmetries in Self-Consistent RPA

It is shown that the Self-Consistent RPA (SCRPA) approach allows in a very natural way to restore symmetries, spontaneously broken on the mean field level. This is achieved via the introduction of a second Lagrange multiplier which constrains the variance of the symmetry operator to zero. This important feature of SCRPA, here pointed out for the first time, is illustrated employing a simplified model of the nuclear superfluidity.

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