Interplay between chiral and axial symmetries in a SU(2) Nambu--Jona-Lasinio Model with the Polyakov loop

We consider a two flavor Polyakov--Nambu--Jona-Lasinio (PNJL) model where the Lagrangian includes an interaction term that explicitly breaks the U$_A(1)$ anomaly. At finite temperature, the restoration of chiral and axial symmetries, signaled by the behavior of several observables, is investigated. We compare the effects of two regularizations at finite temperature, one of them, that allows high momentum quarks states, leading to the full recovery of chiral symmetry. From the analysis of the behavior of the topological susceptibility and of the mesonic masses of the axial partners, it is found in the SU(2) model that, unlike the SU(3) results, the recovery of the axial symmetry is not a consequence of the full recovery of the chiral symmetry. Thus, one needs to use an additional idea, by means of a temperature dependence of the anomaly coefficient, that simulates instanton suppression effects.Comment: 21 pages, 5 figures; PRD versio

How the Polyakov loop and the regularization affect strangeness and restoration of symmetries at finite T

The effects of the Polyakov loop and of a regularization procedure that allows the presence of high momentum quark states at finite temperature is investigated within the Polyakov-loop extended Nambu--Jona-Lasinio model. The characteristic temperatures, as well as the behavior of observables that signal deconfinement and restoration of chiral and axial symmetries, are analyzed, paying special attention to the behavior of strangeness degrees of freedom. We observe that the cumulative effects of the Polyakov loop and of the regularization procedure contribute to a better description of the thermodynamics, as compared with lattice estimations. We find a faster partial restoration of chiral symmetry and the restoration of the axial symmetry appears as a natural consequence of the full recovering of the chiral symmetry that was dynamically broken. These results show the relevance of the effects of the interplay among the Polyakov loop dynamics, the high momentum quark sates and the restoration of the chiral and axial symmetries at finite temperature.Comment: Talk given at XIII International Conference on Hadron Spectroscopy (Hadron 2009), Tallahassee, Florida, USA, 29 Nov - 4 Dec, 200

The QCD Critical End Point in the Context of the Polyakov--Nambu--Jona-Lasinio Model

We investigate the phase diagram of the so-called Polyakov--Nambu--Jona-Lasinio model at finite temperature and nonzero chemical potential with three quark flavors. Chiral and deconfinement phase transitions are discussed, and the relevant order-like parameters are analyzed. A special attention is payed to the critical end point (CEP): the influence of the strangeness on the location of the CEP is studied; also the strength of the flavor-mixing interaction alters the CEP location, once when it becomes weaker the CEP moves to low temperatures and can even disappear.Comment: Prepared for Strangeness in Quark Matter 2011, Sept. 18--24, Cracow, Polan

Exploring the role of model parameters and regularization procedures in the thermodynamics of the PNJL model

The equation of state and the critical behavior around the critical end point are studied in the context of the Polyakov--Nambu--Jona--Lasinio model. We prove that a convenient choice of the model parameters is crucial to get the correct description of isentropic trajectories. The physical relevance of the effects of the regularization procedure is insured by the agreement with general thermodynamic requirements. The results are compared with simple thermodynamic expectations and lattice data.Comment: Talk given at XIII International Conference on Hadron Spectroscopy (Hadron 2009), Tallahassee, Florida, USA, 29 Nov - 4 Dec, 200