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Abdellatif Abada

Publications and source records attributed to Abdellatif Abada.

13 recordsLinked to original sources
arXiv1997

Disoriented chiral condensate formation from tubes of hot quark plasma

We investigate the time evolution of a system of quarks interacting with sigma and pion fields starting from an initial configuration consisting of a tube of hot quark plasma undergoing a boost-invariant longitudinal expansion. We work within the framework of the linear sigma model using classical transport equations for the quarks coupled to the mean-field equations for the meson fields. In certain cases we find strong amplifications of any initial pion fields. For large-radius tubes, starting from quark densities that are very close to critical, we find that a disoriented chiral condensate can form in the centre of the tube. Eventually the collapse of the tube drives this state back to the true vacuum. This process converts the disoriented condensate, dominated by long-wavelength pion modes, into a coherent excitation of the pion field that includes significant components with transverse momenta of around 400 MeV. In contrast, for narrow tubes or larger initial temperatures, amplification occurs only via the pion-laser-like mechanism found previously for spherical systems. In addition, we find that explicit chiral symmetry breaking significantly suppresses the formation of disoriented condensates.

hep-ph↗
arXiv1997

Isoscalar NN spin-orbit potential from a Skyrme model with scalar mesons

As a first step toward circumventing the difficulty to obtain an attractive isospin-independent NN spin-orbit force from Skyrme-type models involving only pions, we investigate an improved Skyrme Lagrangian that incorporates the scalar-isoscalar meson εwhich can be viewed as the cause behind the enhancement of the $ππS$-wave. We find that at large distances, the main contribution to the spin-orbit potential comes from the scalar Lagrangian and it is found to be attractive. We briefly discuss how to pursue this work to finally obtain a medium-range attractive interaction.

hep-ph↗
arXiv1996

Coherent amplification of classical pion fields during the cooling of droplets of quark plasma

In the framework of the linear sigma model, we study the time evolution of a system of classical $σ$ and pion fields coupled to quarks. For this purpose we solve numerically the classical transport equation for relativistic quarks coupled to the nonlinear Klein-Gordon equations for the meson fields. We examine evolution starting from variety of initial conditions corresponding to spherical droplets of hot quark matter, which might mimic the behaviour of a quark plasma produced in high-energy nucleus-nucleus collisions. For large droplets we find a strong amplification of the pion field that oscillates in time. This leads to a coherent production of pions with a particular isospin and so would have similar observable effects to a disoriented chiral condensate which various authors have suggested might be a signal of the chiral phase transition. The mechanism for amplification of the pion field found here does not rely on this phase transition and is better thought of as a "pion laser" which is driven by large oscillations of the $σ$ field.

hep-ph↗
arXiv1996

Comment on ``Relativistic kinetic equations for electromagnetic, scalar and pseudoscalar interactions''

It is found that the extra quantum constraints to the spinor components of the equal-time Wigner function given in a recent paper by Zhuang and Heinz should vanish identically. We point out here the origin of the error and give an interpretation of the result. However, the principal idea of obtaining a complete equal-time transport theory by energy averaging the covariant theory remains valid. The classical transport equation for the spin density is also found to be incorrect. We give here the correct form of that equation and discuss briefly its structure.

hep-ph↗
arXiv1996

On the Skyrme model prediction for the N-N spin-orbit force

In the framework of the product ansatz as an approximation for the two-baryon system we review in details the derivation of the isoscalar nucleon-nucleon spin orbit potential coming from the sixth order term of the extended Skyrme model. We show that the sixth order term contributes with a positive sign, as is the case for the Skyrme term, contrary to the claims of Riska and Schwesinger. Those authors considered only one part of the force due to the sixth order term and omitted the second part which turns out to be the dominant one. Our result is independent of the parameters of the model.

hep-ph↗
arXiv1995

Strangeness content of the nucleon within the NJL soliton model

We investigated the form factors of the nucleon associated with the nonet vector current in the framework of the generalized Yabu--Ando approach to the chiral soliton of the Nambu--Jona--Lasinio model. We introduce a variational parameter to improve the predictions for the baryon mass splittings and, in addition, we take into account $1/N_c$ rotational corrections to accommodate the empirical isovector magnetic moment of the nucleon. We find that the strange magnetic moment lies between -0.05 and 0.25.

hep-ph↗
arXiv1995

Chiral phase transition in an expanding quark antiquark plasma

We investigate the time evolution of a quark antiquark plasma by solving numerically the relativistic transport equations derived on the Hartree level from the Nambu-Jona-Lasinio model. We find that the phase transition in the expanding quark antiquark plasma is different as compared to that in a static plasma. The expansion competes with the transition and finally quark droplets will be formed which subsequently hadronizes. These findings raise the question whether static thermal models can make at all any prediction about signals of that transition .

hep-ph↗
arXiv1995

The giant resonances in hot nuclei: linear response calculations

We calculate the isovector response function of hot nuclear matter using various effective Skyrme interactions. For Skyrme forces with a small effective mass the strength distribution is found to be nearly independent of temperature, and shows little collective effects. In contrast effective forces with an effective mass close to unity produce sizeable collective effects at zero temperature which disappear at temperatures of a few MeV. We discuss the relevance of these results for the saturation of the multiplicity of photons emitted by the giant dipole resonance in hot nuclei beyond $T$=3 MeV observed in recent experiments.

nucl-th↗
arXiv1994

The Isospin Independent Spin-Orbit Force in the Extended Skyrme Model

By using the product ansatz as an approximation for the two-baryon system we investigate the isoscalar nucleon-nucleon spin-orbit potential in an extended Skyrme model including both fourth- and sixth-order terms. As it is the case for the Skyrme model, we still obtain the wrong sign for this interaction. Nevertheless, concerning the order of magnitude, the extended Skyrme model provides a better agreement with phenomenological potentials, as compared to the standard one.

hep-ph↗
arXiv1993

Effective Lagrangian with vector mesons : Linear response theory

The soliton breathing mode is investigated in the framework of linear response theory within a Skyrme model vector meson stabilized. The effective Lagrangian considered includes the $ρ$ (introduced following the standard prescription of nonlinear chiral symmetry) and the $ω$ mesons. The monopole response function is found to have a pronounced peak which is identified to the $P11$ (Roper) resonance. The results are compared to those obtained within the local approximation.

hep-ph↗
arXiv1993

Two-Phonon States in Alkali-Metal Clusters

Two phonon-states of alkali-metal clusters (treated as jellium spheres) are calculated by using a method based on a perturbative construction of periodic orbits of the time-dependent mean-field equations. Collective vibrations with various multipolarities in charged $Na^+_{21}$ are considered.

cond-mat↗
arXiv1993

The Breathing Mode in Extended Skyrme Model

We study an extended Skyrme model which includes fourth and sixth-order terms. We explore some static properties like the $Δ$-nucleon mass splitting and investigate the Skyrmion breathing mode in the framework of the linear response theory. We find that the monopole response function has a pronounced peak located at $\sim$ 400 MeV, which we identify to the Roper resonance $N(1440)$. As compared to the standard one, the extended Skyrme model provides a more accurate description of baryon properties.

hep-ph↗