Phase structure in a hadronic chiral model

Abstract

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.Understanding hot and baryon-dense QCD matter is of central importance in theoretical and experimental heavy-ion physics. Various effective theories for chiral symmetry restoration predict that a line of first-order phase transitions in the plane of quark-chemical potential µ q versus temperature T ends in a critical point as the chemical potential is lowered (see [1] for a review). Presently, the lattice locates that point at T ≈ 160 MeV, µ q ≈ 120 MeV [2]. The Compressed Baryonic Matter (CBM) experiment at GSI FAIR is planned to perform a dedicated experimental effort to detect that line of firstorder phase transitions in relativistic heavy-ion collisions. It is hoped that by varying experimental parameters like the beam energy one could trigger phase transitions of variable strength (latent heat) and perhaps even locate the expected second-order critical point.Models relying exclusively on order-parameter dynamics typically predict significantly lower chiral phase transition temperatures in baryon-dense matter than those found on the lattice (see e.g. Fig. 6 in [1]). As shown by Gerber and Leutwyler some time ago [3], while heavy hadronic states are suppressed by the Boltzmann factor, their contribution to the energy density at high temperature is substantial. This agrees with other studies using a hadron resonance gas approach, which provides a reasonable description of the thermodynamics obtained on the lattice below the critical temperature [4]. Heavy states also reduce [3] the strong dependence of the "critical temperature" (defined via the peak of a suitable susceptibility) on the pion mass obtained in simple models for chiral order parameter dynamics [5]. The lattice indicates a relatively weak dependence of T c on the pion mass [6].In this Letter we investigate the role of heavy hadronic states on the location of the chiral critical point within a non-linear SU (3) L × SU (3) R chiral model [7]. Here, the phase transition at high temperature and baryon density is "driven" by baryonic resonance degrees of freedom, as suggested by the discussion above. We shall show that the model is able to reproduce not only the sketched qualitative phase structure but also the location of the endpoint. The properties of the high mass states (masses and couplings) are important for the actual location of the chiral phase transition line [8] in the plane of T and µ q .Lattice results show that the susceptibility peaks of the chiral condensate and of the Polyakov loop coincide at µ q = 0 [9] which indicates that for small µ q those transition(s) involve a coupling of the chiral dynamics to the gauge fields, see e.g. [10]. However, within a matrix model for Polyakov loops, the effect of µ q > 0 on the critical t...

Proto–Neutron and Neutron Stars in a Chiral SU(3) Model

“…The model is extended to include effects from the lowest spin-3/2 baryonic multiplet. The model has been successfully applied to the description of nuclear matter and finite nuclei (Papazoglou et al 1998(Papazoglou et al , 1999, as well as to the high-temperature and high-density environment of an ultrarelativistic heavy-ion collision (Zschiesche et al 2007). A study of neutron stars had also been performed (Hanauske et al 2000;Schramm & Zschiesche 2003).…”

Critical endpoint in the Polyakov-loop extended NJL model

“…It is also known in the chiral hadron model [11,12] that a CEP appears at T much higher than the prediction of the NJL model. This implies that the deconfinement phase transition plays an important role in determining the position of the CEP.…”

(3+1)-dimensional hydrodynamic expansion with a critical point from realistic initial conditions

“…[53]. Note that although the present model and parametrization of the EOS are identical to those in Refs.…”