Abstract
We study the bulk and shear viscosity and the electrical conductivity in a quasiparticle approach to Yang-Mills theory and QCD with light and strange quarks to assess the dynamical role of quarks in transport properties at finite temperature. The interactions with a hot medium are embodied in effective masses of the constituents through a temperature-dependent running coupling extracted from the lattice QCD thermodynamics. In Yang-Mills theory, the bulk viscosity to entropy density ratio exhibits a non-monotonous structure around the phase transition temperature. In QCD, this is totally dissolved because of a substantial contribution from quark quasiparticles. The bulk to shear viscosity ratio near the phase transition behaves consistently to the scaling with the speed of sound derived in the AdS/CFT approach, whereas at high temperature it obeys the same parametric dependence as in perturbation theory. Thus, the employed quasiparticle model is adequate to capture the transport properties in the weak and strong coupling regimes of the theory. This feature is not altered by including dynamical quarks which, however, retards the system from restoring conformal invariance. We also examine the individual flavor contributions to the electrical conductivity and show that the obtained behavior agrees qualitatively well with the recent results of lattice simulations and with a class of phenomenological approaches.
Highlights
Two decades of intensive theoretical explorations of the flow observables in ideal [1,2,3,4,5] and viscous [6,7,8,9,10,11,12,13] hydrodynamics have successfully delineated the quark gluon plasma (QGP) created at the Relativistic Heavy Ion Collider (RHIC) and LHC as a strongly coupled fluid
It has been shown in a quasiparticle model [21] that, near the phase transition, the bulk to shear viscosity ratio of a gluon plasma decreases as predicted in the AdS=CFT approach, whereas at a higher temperature as in perturbative QCD
We have examined the transport coefficients, the bulk ζ and shear η viscosity, and the electrical conductivity σ of deconfined strongly interacting matter in pure Yang–Mills theory and QCD with Nf 1⁄4 2 þ 1 at vanishing chemical potential
Summary
Two decades of intensive theoretical explorations of the flow observables in ideal [1,2,3,4,5] and viscous [6,7,8,9,10,11,12,13] hydrodynamics have successfully delineated the quark gluon plasma (QGP) created at the Relativistic Heavy Ion Collider (RHIC) and LHC as a strongly coupled fluid. The dynamic criticality of the bulk viscosity has been discussed as a probe of a QCD critical point [29,42] It has been shown in a quasiparticle model [21] that, near the phase transition, the bulk to shear viscosity ratio of a gluon plasma decreases as predicted in the AdS=CFT approach, whereas at a higher temperature as in perturbative QCD (pQCD). The precise determination of the transport parameters as functions of temperature and chemical potential, as well as their incorporation to the fluid dynamical simulations, is one of the main steps towards understanding the nontrivial evolution of strongly interacting matter This requires comprehension of the dynamical role of light and strange quark quasiparticles on the transport properties.
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