A dynamical quasiparticle approach for the Quark-Gluon-Plasma bulk and transport properties

Abstract

The properties of quantum-chromo dynamics (QCD) nowadays are accessable by lattice QCD calculations at vanishing quark chemical potential $\mu_q$=0 but often lack a transparent physical interpretation. In this review we report about results from an extended dynamical quasiparticle model (DQPM$^*$) in which the effective parton propagators have a complex selfenergy that depends on the temperature $T$ of the medium as well as on the chemical potential $\mu_q$ and the parton three-momentum ${\boldsymbol p}$ with respect to the medium at rest. It is demonstrated that this approach allows for a good description of QCD thermodynamics with respect to the entropy density, pressure etc. above the critical temperature $T_c \approx$ 158 MeV. Furthermore, the quark susceptibility $\chi_q$ and the quark number density $n_q$ are found to be reproduced simultaneously at zero and finite quark chemical potential. The shear and bulk viscosities $\eta, \zeta$, and the electric conductivity $\sigma_e$ from the DQPM$^*$ also turn out in close agreement with lattice results for $\mu_q$ =0. The DQPM$^*$, furthermore, allows to evaluate the momentum $p$, $T$ and $\mu_q$ dependencies of the partonic degrees of freedom also for larger $\mu_q$ which are mandatory for transport studies of heavy-ion collisions in the regime 5 GeV $< \sqrt{s_{NN}} <$ 10 GeV. We finally calculate the charm quark diffusion coefficient $D_s$ -- evaluated from the differential cross sections of partons in the medium for light and heavy quarks by employing the propagators and couplings from the DQPM -- and compare to the available lattice data. It is argued that the complete set of observables allows for a transparent interpretation of the properties of hot QCD.