Impact of baryon resonances on the chiral phase transition at finite temperature and density

We study the phase diagram of a generalized chiral SU(3)-flavor model in mean-field approximation. In particular, the influence of the baryon resonances, and their couplings to the scalar and vector fields, on the characteristics of the chiral phase transition as a function of temperature and baryon-chemical potential is investigated. Present and future finite-density lattice calculations might constrain the couplings of the fields to the baryons. The results are compared to recent lattice QCD calculations and it is shown that it is non-trivial to obtain, simultaneously, stable cold nuclear matter.Comment: 18 pages, 7 figure

In-medium vector meson masses in a Chiral SU(3) model

A significant drop of the vector meson masses in nuclear matter is observed in a chiral SU(3) model due to the effects of the baryon Dirac sea. This is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation. The appreciable decrease of the in-medium vector meson masses is due to the vacuum polarisation effects from the nucleon sector and is not observed in the mean field approximation.Comment: 26 pages including 10 figures; the text has been modified for clarit

Nuclear and Neutron Star Radii

We investigate the correlation between nuclear neutron radii and the radius of neutron stars. We use a well-established hadronic SU(3) model based on chiral symmetry that naturally includes non-linear vector meson and scalar meson - vector meson couplings. The relative strengths of the couplings modify the nuclear isospin-dependent interactions. We study the dependence of nuclear and neutron star radii on the coupling strengths. The relevance of the results for parity-violating electron-nucleus scattering and the URCA process in neutron stars is discussed

Phase Structure in a Hadronic Chiral Model

We study the phase diagram of a hadronic chiral flavor-SU(3) model. Heavy baryon resonances can induce a phase structure that matches current results from lattice-QCD calculations at finite temperature and baryon density. Furthermore, we determine trajectories of constant entropy per net baryon in the phase diagram.Comment: 4 pages, 5 figure

Critical Review Of Quark Gluon Plasma Signals

Compelling evidence for a new form of matter has been claimed to be formed in Pb+Pb collisions at SPS. We critically review two suggested signatures for this new state of matter: First the suppression of the J/$\Psi$, which should be strongly suppressed in the QGP by two different mechanisms, the color-screening and the QCD-photoeffect. Secondly the measured particle, in particular strange hadronic, ratios might signal the freeze-out from a quark-gluon phase.Comment: 7 pages 6 figures, Contribution to the Proceedings of CRIS 2000, 3rd Catania Relativistic Ion Studies, Acicastello, Italy, May 22-26, 200

Particle ratios at RHIC: Effective hadron masses and chemical freeze-out

The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU(3) \sigma-\omega approach. The commonly adopted noninteracting gas calculations yield temperatures close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. Contrary, the chiral SU(3) model predicts temperature and density dependent effective hadron masses and effective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three different parametrizations of the model, which show different types of phase transition behaviour, are investigated. We show that if a chiral phase transition occured in those collisions, ''freezing'' of the relative hadron abundances in the symmetric phase is excluded by the data. Therefore, either very rapid chemical equilibration must occur in the broken phase, or the measured hadron ratios are the outcome of the dynamical symmetry breaking. Furthermore, the extracted chemical freeze-out parameters differ considerably from those obtained in simple noninteracting gas calculations. In particular, the three models yield up to 35 MeV lower temperatures than the free gas approximation. The in-medium masses turn out differ up to 150 MeV from their vacuum values.Comment: 13 pages, 4 figure

Effects of Dirac sea polarization on hadronic properties - A chiral SU(3) approach

The effect of vacuum fluctuations on the in-medium hadronic properties is investigated using a chiral SU(3) model in the nonlinear realization. The effect of the baryon Dirac sea is seen to modify hadronic properties and in contrast to a calculation in mean field approximation it is seen to give rise to a significant drop of the vector meson masses in hot and dense matter. This effect is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation (RHA), where the baryon self energy is modified due to interactions with both the non-strange $(\sigma)$ and the strange $(\zeta)$ scalar fields.Comment: 25 pages including 13 figures,figure styles modified,few clarifying sentences added in text, to appear in Phys. Rev.

Current Status of Quark Gluon Plasma Signals

Compelling evidence for the creation of a new form of matter has been claimed to be found in Pb+Pb collisions at SPS. We discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions. It is demonstrated that so far none of the proposed signals like J\psi meson production/suppression, strangeness enhancement, dileptons, and directed flow unambigiously show that a phase of deconfined matter has been formed in SPS Pb+Pb collisions. We emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from data.Comment: 12 pages, 6 figures, Proceedings of the Symposium on Fundamental Issues in Elementary Matter In Honor and Memory of Michael Danos 241. WE-Heraeus-Seminar Bad Honnef, Germany, 25--29 September 2000. To appear in Heavy Ion Phy