QCD & QGP: A Summary

2013

A combined effective model reproducing the equation of state of hadronic matter as obtained in recent lattice QCD simulations is presented. The model reproduces basic physical characteristics encountered in dense hadronic matter in the quark-gluon plasma (QGP) phase and the lower temperature hadron resonance gas phase. The hadronic phase is described by means of an extended Mott-Hagedorn resonance gas while the QGP phase is described by the extended PNJL model. The dissociation of hadrons is obtained by including the state dependent hadron resonance width.

Nuclear Physics B, 2002

The phase diagram of two-color QCD as a function of temperature and baryon chemical potential is considered. Using a low-energy chiral Lagrangian based on the symmetries of the microscopic theory, we determine, at the one-loop level, the temperature dependence of the critical chemical potential for diquark condensation and the temperature dependence of the diquark condensate and baryon density. The prediction for the temperature dependence of the critical chemical potential is consistent with the one obtained for a dilute Bose gas. The associated phase transition is shown to be of second order for low temperatures and first order at higher temperatures. The tricritical point at which the second order phase transition ends is determined. The results are carried over to QCD with quarks in the adjoint representation and to ordinary QCD at a non-zero chemical potential for isospin.

Physical Review D, 1985

Nuclear Physics A, 1994

Two lagrangians, which implement the QCD scale anomaly, are used to study the coupling of quark and gluon condensates in dense and hot matter. The response of the system strongly depends on the assumed value of the vacuum gluon condensate. For a low value of this vacuum gluon condensate, quark and gluon condensates feel simultaneously the chiral phase transition while for a larger value, the gluon condensate keeps its vacuum value and the quark condensate is the only order parameter of the transition. We also calculate in both models the equation of state of nuclear matter.

2009

We present the latest results for the equation of state and the crossover transition in 2+1 flavor QCD from the HotQCD Collaboration. Bulk thermodynamic quantities -energy density, pressure, entropy density, and the speed of sound -are calculated on lattices with temporal extent N t = 8 in the temperature range 140 MeV < T < 540 MeV. We utilize two improved staggered fermion actions, asqtad and p4, with the mass for the two degenerate light quarks chosen to be m ud = 0.1m s , corresponding to m π ≈ 220 MeV for the lightest pion. We also calculate observables that are sensitive to the chiral and deconfing transitions -the light and strange quark number susceptibilities, the chiral condensate, and the renormalized Polyakov loop -finding that deconfinement and chiral symmetry restoration occur in the same narrow temperature interval.

Physics Letters B, 2004

International Journal of Modern Physics A, 2013

The ultimate aim of high energy heavy ion collisions is to study quark deconfinement and the quark–gluon plasma predicted by quantum chromodynamics. This requires the identification of observables calculable in QCD and measurable in heavy ion collisions. I concentrate on three such phenomena, related to specific features of strongly interacting matter. The observed pattern of hadrosynthesis corresponds to that of an ideal resonance gas in equilibrium at the pseudo-critical temperature determined in QCD. The critical behavior of QCD is encoded in the fluctuation patterns of conserved quantum numbers, which are presently being measured. The temperature of the quark–gluon plasma can be determined by the dissociation patterns of the different quarkonium states, now under study at the LHC for both charmonia and bottomonia.

Physical Review D, 2013

The finite temperature chiral condensate for 2 + 1 quark flavors is considered in the framework of the hadron resonance gas model. This requires some dynamical information, for which two models are employed: one based on the quark structure of hadrons combined with the Nambu-Jona-Lasinio approach to chiral symmetry breaking, and one originating from gauge/gravity duality. Using these insights, hadronic sigma terms are discussed in the context of recent first principles results following from lattice QCD and chiral perturbation theory. For the condensate, in generic agreement with lattice data it is found that chiral symmetry restoration in the strange quark sector takes place at higher temperatures than in the light quark sector. The importance of this result for a recently proposed dynamical model of hadronic freeze-out in heavy-ion collisions is outlined.

Physical Review D, 2016

We show how a scheme of rewriting a divergent momentum integral can conciliate results obtained with the Nambu-Jona-Lasinio model and recent lattice results for the chiral transition in the presence of a chiral imbalance in quark matter. Purely vacuum contributions are separated from mediumdependent regularized momentum integrals in such a way that one is left with ultraviolet divergent momentum integrals that depend on vacuum quantities only. The scheme is applicable to other commonly used effective models to study quark matter with a chiral imbalance, it allows us to identify the source of their difficulties in reproducing the qualitative features of lattice results, and enhances their predictability and uses in other applications.

2013

Using a unified hadron-quark effective model for the QCD equation of state, this paper studies the phase structure of strongly interacting matter in a wide range of temperature and baryonchemical potential. At small potentials the model yields a smooth cross-over to chirally restored matter with a transition temperature and curvature in line with recent lattice QCD estimates and thermal model fits of freeze-out curves. Trajectories of constant entropy per net baryon number show a clear dependence on the particle composition in the model and on repulsive vector field interactions. Although the model might feature a critical end-point at a rather high baryonchemical potential and low temperature, probing it in heavy-ion collisions might be highly challenging due to a large thermodynamic spread of matter in the collision fireball.