OPUS 4 Latest Documents RSS FeedLatest documents
http://publikationen.ub.uni-frankfurt.de/index/index/
Thu, 19 Jan 2006 14:26:55 +0100Thu, 19 Jan 2006 14:26:55 +0100Phase transition in the chiral sigma-omega model with dilatons
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3002
We investigate the properties of di erent modifications to the linear -model (including a dilaton field associated with broken scale invariance) at finite baryon density and nonzero temperature T. The explicit breaking of chiral symmetry and the way the vector meson mass is generated are significant for the appearance of a phase of nearly vanishing nucleon mass besides the solution describing normal nuclear matter. The elimination of the abnormal solution prohibits the onset of a chiral phase transition but allows to lower the compressibility to a reasonable range. The repulsive contributions from the vector mesons are responsible for the wide range of stability of the normal phase in the (µ, T)-plane. The abnormal solution becomes not only energet- ically preferable to the normal state at high temperature or density, but also mechanically stable due to the inclusion of dilatons. PACS number:12.39.FPanajotis Papazoglou; Jürgen Schaffner; Stefan Schramm; Detlef Zschiesche; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3002Thu, 19 Jan 2006 14:26:55 +0100Hypermatter in chiral field theory
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3038
Abstract. A generalized Lagrangian for the description of hadronic matter based on the linear SU(3)L × SU(3)R -model is proposed. Besides the baryon octet, the spin-0 and spin-1 nonets, a gluon condensate associated with broken scale invariance is incorporated. The observed values for the vacuum masses of the baryons and mesons are reproduced. In mean-field approximation, vector and scalar interactions yield a saturating nuclear equation of state. Finite nuclei can be reasonably described, too. The condensates and the e ective baryon masses at finite baryon density and temperature are discussed.Panajotis Papazoglou; Detlef Zschiesche; Stefan Schramm; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3038Thu, 05 Jan 2006 09:33:08 +0100Nuclei in a chiral SU(3) model
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3099
Nuclei can be described satisfactorily in a nonlinear chiral SU(3)-framework, even with standard potentials of the linearmodel. The condensate value of the strange scalar meson is found to be important for the properties of nuclei even without adding hyperons. By neglecting terms which couple the strange to the nonstrange condensate one can reduce the model to a Walecka model structure embedded in SU(3). We discuss inherent problems with chiral SU(3) models regarding hyperon optical potentials.Panajotis Papazoglou; Detlef Zschiesche; Stefan Schramm; Jürgen Schaffner-Bielich; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3099Mon, 12 Dec 2005 10:29:16 +0100Chiral model for dense, hot and strange hadronic matter
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3145
Introduction: Until now it is not possible to determine the equation of state (EOS) of hadronic matter from QCD. One succesfully applied alternative way to describe the hadronic world at high densities and temperatures are effective models like the RMF-models [1], where the relevant degrees of freedom are baryons and mesons instead of quarks and gluons. Since approximate chiral symmetry is an essential feature of QCD, it should be a useful concept for building and restricting e ective models. It has been shown [2,3] that effective sigma-omega models including SU(2) chiral symmetry are able to obtain a reasonable description of nuclear matter and finite nuclei. Recently [4] we have shown that an extended SU(3) × SU(3) chiral sigma-omega model is able to describe nuclear matter ground state properties, vacuum properties and finite nuclei satisfactorily. This model includes the lowest SU(3) multiplets of the baryons (octet and decuplet[5]), the spin-0 and the spin-1 mesons as the relevant degrees of freedom. Here we will discuss the predictions of this model for dense, hot, and strange hadronic matter.Detlef Zschiesche; Panajotis Papazoglou; Christian W. Beckmann; Stefan Schramm; Jürgen Schaffner-Bielich; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3145Tue, 29 Nov 2005 10:40:12 +0100Neutron star properties in a chiral SU(3) model
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3153
We investigate various properties of neutron star matter within an e ective chiral SU(3)L × SU(3)R model. The predictions of this model are compared with a Walecka-type model. It is demonstrated that the importance of hy- peron degrees are strongly depending on the interaction used, even if the equation of state near saturation density is nearly the same in both models. While the Walecka-type model predicts a strange star core with strangeness fraction fS 4/3, the chiral model allows only for fS 1/3 and predicts that 0, + and 0 will not exist in star, in contrast to the Walecka-type model. PACS: 26.60+c, 21.65+f, 24.10JvMatthias Hanauske; Detlef Zschiesche; Subrata Pal; Stefan Schramm; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3153Thu, 24 Nov 2005 10:44:38 +0100Hadrons in dense resonance matter: a chiral SU(3) approach
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3184
A nonlinear chiral SU(3) approach including the spin 3 2 decuplet is developed to describe dense matter. The coupling constants of the baryon resonances to the scalar mesons are determined from the decuplet vacuum masses and SU(3) symmetry relations. Di erent methods of mass generation show significant differences in the properties of the spin- 3 2 particles and in the nuclear equation of stateDetlef Zschiesche; Panajotis Papazoglou; Stefan Schramm; Jürgen Schaffner-Bielich; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3184Wed, 23 Nov 2005 11:28:55 +0100Superheavy nuclei in a chiral hadronic model
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3182
Superheavy nuclei are investigated in a nonlinear chiral SU(3)-model. The proton number Z=120 and neutron numbers of N=172, 184 and 198 are predicted to be magic. The charge distributions and alpha-decay chains hint towards a hollow stucture.Christian Beckmann; Panajotis Papazoglou; Detlef Zschiesche; Stefan Schramm; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3182Wed, 23 Nov 2005 10:13:43 +0100Critical review of quark gluon plasma signals
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3186
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 [1] and the QCD-photoe ect [2]. Secondly the measured particle, in particular strange hadronic, ratios might signal the freeze-out from a quark-gluon phase.Detlef Zschiesche; Lars Gerland; Stefan Schramm; Jürgen Schaffner-Bielich; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3186Wed, 23 Nov 2005 09:19:04 +0100Nuclei, superheavy nuclei, and hypermatter in a chiral SU(3) model
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3259
A model based on chiral SU(3)-symmetry in nonlinear realisation is used for the investigation of nuclei, superheavy nuclei, hypernuclei and multistrange nuclear objects (so called MEMOs). The model works very well in the case of nuclei and hypernuclei with one Lambda-particle and rules out MEMOs. Basic observables which are known for nuclei and hypernuclei are reproduced satisfactorily. The model predicts Z=120 and N=172, 184 and 198 as the next shell closures in the region of superheavy nuclei. The calculations have been performed in self-consistent relativistic mean field approximation assuming spherical symmetry. The parameters were adapted to known nuclei.Christian Beckmann; Panajotis Papazoglou; Detlef Zschiesche; Stefan Schramm; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3259Thu, 17 Nov 2005 13:07:00 +0100Space-time evolution and HBT analysis of relativistic heavy ion collisions in a chiral SU(3) x SU(3) model
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3264
The space-time dynamics and pion-HBT radii in central heavy ion-collisions at CERN-SPS and BNL-RHIC are investigated within a hydrodynamic simulation. The dependence of the dynamics and the HBT-parameters on the EoS is studied with different parametrizations of a chiral SU(3) sigma omega model. The selfconsistent collective expansion includes the e ects of e ective hadron masses, generated by the nonstrange and strange scalar condensates. Different chiral EoS show di erent types of phase transitions and even a crossover. The influence of the order of the phase transition and of the latent heat on the space-time dynamics and pion-HBT radii is studied. A small latent heat, i.e. a weak first-order chiral phase transition, or a smooth crossover lead to distinctly di erent HBT predictions than a strong first order phase transition. A quantitative description of the data, both at SPS energies as well as at RHIC energies, appears di cult to achieve within the ideal hydrodynamic approach using the SU(3) chiral EoS. A strong first-order quasi-adiabatic chiral phase transition seems to be disfavored by the pion-HBT data from CERN-SPS and BNL-RHIC.Detlef Zschiesche; Stefan Schramm; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3264Thu, 17 Nov 2005 11:02:36 +0100Particle ratios at RHIC : effective hadron masses and chemical freeze-out
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3288
The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU(3) theta - 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 e ective hadron masses and e ective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three di erent parametrizations of the model, which show di erent 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 di er 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 di er up to 150 MeV from their vacuum values.Detlef Zschiesche; Stefan Schramm; Jürgen Schaffner-Bielich; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3288Tue, 15 Nov 2005 11:49:54 +0100In-medium vector meson masses in a chiral SU(3) model
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3303
A significant drop of the vector meson masses in nuclear matter is observed in a chiral SU(3) model due to the e ects 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 e ects from the nucleon sector and is not observed in the mean field approximation.Detlef Zschiesche; Amruta Mishra; Stefan Schramm; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3303Mon, 14 Nov 2005 10:38:37 +0100Effects of Dirac sea polarization on hadronic properties : a Chiral SU(3) approach
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3325
Abstract: The e ect of vacuum fluctuations on the in-medium hadronic properties is investigated using a chiral SU(3) model in the nonlinear realization. The e ect 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 e ect 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 ( ) and the strange ( ) scalar fields.Amruta Mishra; K. Balazs; Detlef Zschiesche; Stefan Schramm; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3325Thu, 10 Nov 2005 10:29:25 +0100Particle ratios from AGS to RHIC in an interacting hadronic model
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3316
Abstract: The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU(3) Ã É approach. The commonly adopted non-interacting gas calculations yield temperatures close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. In contrast, 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 non-interacting gas calculations. In particular, the three models yield up to 35 MeV lower temperatures than the free gas approximation. The inmedium masses turn out to differ up to 150 MeV from their vacuum values.Detlef Zschiesche; Gebhard Zeeb; Kerstin Paech; Horst Stöcker; Stefan Schrammarticlehttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3316Wed, 09 Nov 2005 11:21:07 +0100Impact of baryon resonances on the chiral phase transition at finite temperature and density
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3345
We study the phase diagram of a generalized chiral SU(3)-flavor model in mean-field approxi- mation. 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.Detlef Zschiesche; Gebhard Zeeb; Stefan Schramm; Horst Stöckerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3345Wed, 09 Nov 2005 09:22:24 +0100Physics opportunities at RHIC and LHC
http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3367
Nonequilibrium models (three-fluid hydrodynamics, UrQMD, and quark molecular dynamics) are used to discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions from the SPS via RHIC to LHC. It is demonstrated that these models - although they do treat the most interesting early phase of the collisions quite differently (thermalizing QGP vs. coherent color fields with virtual particles) -- all yield a reasonable agreement with a large variety of the available heavy ion data. Hadron/hyperon yields, including J/Psi meson production/suppression, strange matter formation, dileptons, and directed flow (bounce-off and squeeze-out) are investigated. Observations of interesting phenomena in dense matter are reported. However, 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. The role of future experiments with the STAR and ALICE detectors is pointed out.Stefan Scherer; Steffen A. Bass; Mohamed Belkacem; Marcus Bleicher; Jörg Brachmann; Adrian Dumitru; Christoph Ernst; Lars Gerland; Nils Hammon; Markus Hofmann; Jens Konopka; Ludwig Neise; Manuel Reiter; Stefan Schramm; Sven Soff; Christian Spieles; Henning Weber; Detlef Zschiesche; Joachim A. Maruhn; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3367Tue, 01 Nov 2005 09:26:33 +0100