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

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

Ground State Properties and Glueball Spectrum in SU(2) Yang-Mills Theory using Gauge Invariant Variables

We describe a nonperturbative calculation of the spectrum of SU(2) Yang-Mills theory based on a Hamiltonian formulation. Our approach exploits gauge invariant variables similar to those used in nuclear physics to describe collective motion in nuclei.Comment: 18 pages Late

The transition temperature of the dilute interacting Bose gas

We show that the critical temperature of a uniform dilute Bose gas must increase linearly with the s-wave scattering length describing the repulsion between the particles. Because of infrared divergences, the magnitude of the shift cannot be obtained from perturbation theory, even in the weak coupling regime; rather, it is proportional to the size of the critical region in momentum space. By means of a self-consistent calculation of the quasiparticle spectrum at low momenta at the transition, we find an estimate of the effect in reasonable agreement with numerical simulations.Comment: 4 pages, Revtex, to be published in Physical Review Letter

METHODES VARIATIONNELLES ET INVARIANCE DE JAUGE (VERS UNE ETUDE NON PERTURBATIVE DES THEORIES DE YANG-MILLS EN DIMENSION 4)

PARIS-BIUSJ-Physique recherche (751052113) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocSudocFranceF

Propagation of a Pionium Inside Matter

peer reviewe

Boost Invariant Quantum Evolution of a Meson Field At Large Proper Times

We construct asymptotic solutions of the functional Schrodinger 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. Unit'e de Recherche des Universit'es Paris XI et Paris VI associ'ee au C.N.R.S Introduction. --- Several recent studies have been devoted to the calculation of the evolution of a self interacting scalar field. As an example the evolution of a scalar field is an important ingredient in most inflationary models [1, 2, 3, 4, 5]. Also classical as well as quantum calculations of the evolution of a scalar field have been considered in the context of the possible formation of a disoriented chiral condensate in ultrarelativistic nuclear collisions [6, 7, 8, 9, 10]. In this note we investigate..