Boost invariant quantum evolution of a meson field at large proper times

We construct asymptotic solutions of the functional Schroedinger equation for a scalar field in the Gaussian approximation at large proper time. These solutions describe the late proper time stages of the expansion of a meson gas with boost invariant boundary conditions. The relevance of these solutions for the formation of a disoriented chiral condensate in ultra relativistic collisions is discussed.Comment: 9 pages, LATE

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.Comment: 6 pages, LaTeX file, 3 figures (not included, available on request) (Contribution to the 3th IN2P3-Riken Symposium on Heavy Ion Collisions, Shinrin-Koen, Saitama, Japan, October 1994

Response Function of Hot Nuclear Matter

We investigate the response function of hot nuclear matter to a small isovector external field using a simplified Skyrme interaction reproducing the value of the symmetry energy coefficient. We consider values of the momentum transfer corresponding to the dipole oscillation in heavy nuclei. We find that while at zero temperature the particle hole interaction is almost repulsive enough to have a sharp (zero sound type) collective oscillation, such is no longer the case at temperatures of a few MeV. As a result a broadening of the dipole resonance occurs, leading to its quasi disappearence by the time the temperature reaches 5 MeV. The sensivity of the temperature evolution of the width when modifying the residual interaction strength is also examined.Comment: 9 pages, IPNO/TH 94-15, DPT-IPN Orsay. Two figures available under reques

Du laboratoire audio au laboratoire multimédia

Les évolutions technologiques récentes amènent les enseignants de langues à faire des choix pour intégrer les outils multimédias dans leur pratique. Les investissements qu'implique cette modernisation, tant en termes de budgets qu'en termes de formation des utilisateurs, nécessitent que ces choix soient éclairés. La complexité du domaine appelle la fédération des compétences et la circulation de l'information pour surmonter les obstacles les plus fréquents. On trouvera ci-dessous une contribution à ce débat sous la forme d'un état des lieux dans une université spécialisée dans les langues et de l'examen détaillé d'un aspect particulier assez épineux, mais incontournable, la création de cours multimédias à partir de matériau pédagogique existant

Mean field theory for collective motion of quantum meson fields

Mean field theory for the time evolution of quantum meson fields is studied in terms of the functional Schroedinger picture with a time-dependent Gaussian variational wave functional. We first show that the equations of motion for the variational wavefunctional can be rewritten in a compact form similar to the Hartree-Bogoliubov equations in quantum many-body theory and this result is used to recover the covariance of the theory. We then apply this method to the O(N) model and present analytic solutions of the mean field evolution equations for an N-component scalar field. These solutions correspond to quantum rotations in isospin space and represent generalizations of the classical solutions obtained earlier by Anselm and Ryskin. As compared to classical solutions new effects arise because of the coupling between the average value of the field and its quantum fluctuations. We show how to generalize these solutions to the case of mean field dynamics at finite temperature. The relevance of these solutions for the observation of a coherent collective state or a disoriented chiral condensate in ultra-relativistic nuclear collisions is discussed.Comment: 31 pages, 2 Postscript figures, uses ptptex.st

Temperature dependence of the response function of hot nuclear matter

The description of collective motion in nuclei at finite temperature using the framework of the random phase approximation is discussed. We focus on the special case of the isovector response function of hot nuclear matter using various effective Skyrme interactions

Continuum HFB calculations with finite range pairing interactions

A new method of calculating pairing correlations in coordinate space with finite range interactions is presented. In the Hartree-Fock-Bogoliubov (HFB) approach the mean field part is derived from a Skyrme-type force whereas the pairing field is constructed with a Gogny force. An iterative scheme is used for solving the integro-differential HFB equations via the introduction of a local equivalent potential. The method is illustrated on the case of the nucleus $^{18}$C. It is shown that the results are insensitive to the cut off value in the quasiparticle spectrum if this value is above 100 MeV.Comment: 3 figures, in press, Phys. Lett.

A new baryonic equation of state at sub-nuclear densities for core-collapse simulations

We calculate a new equation of state for baryons at sub-nuclear densities meant for the use in core-collapse simulations of massive stars. The abundance of various nuclei is obtained together with the thermodynamic quantities. The formulation is the NSE description and the liquid drop approximation of nuclei. The model free energy to minimize is calculated by relativistic mean field theory for nucleons and the mass formula for nuclei with the atomic number up to ~ 1000. We have also taken into account the pasta phase, thanks to which the transition to uniform nuclear matter in our EOS occurs in the conventional manner: nuclei are not dissociated to nucleons but survive right up to the transition to uniform nuclear matter. We find that the free energy and other thermodynamical quantities are not very different from those given in the Shen's EOS, one of the standard EOS's that adopt the single nucleus approximation. The average mass is systematically different, on the other hand, which may have an important ramification to the rates of electron captures and coherent neutrino scatterings on nuclei in supernova cores. It is also interesting that the root mean square of the mass number is not very different from the average mass number, since the former is important for the evaluation of coherent scattering rates on nuclei but has been unavailable so far. The EOS table is currently under construction, which will include the weak interaction rates.Comment: 34 pages, 11 figures, Accepted for publication Ap