Abstract
We study the temperature dependence of the shear viscosity to entropy density ratio in pure Yang-Mills theory and in QCD with light and strange quarks within kinetic theory in the relaxation time approximation. As effective degrees of freedom in a deconfined phase we consider quasiparticle excitations with quark and gluon quantum numbers and dispersion relations that depend explicitly on the temperature. The quasiparticle relaxation times are obtained by computing the microscopic two-body scattering amplitudes for the elementary scatterings among the quasiparticles. For pure Yang-Mills theory, we show that the shear viscosity to entropy density ratio exhibits a characteristic nonmonotonicity with a minimum at the first-order phase transition. In the presence of dynamical quarks, the ratio smoothens while still exhibiting a minimum near confinement. Furthermore, there is a significant increase of the shear viscosity to entropy density ratio in QCD resulting from the quark contributions. This observation differs from previously reported estimates based on functional methods but is in line with perturbative QCD expectations at higher temperatures.
Highlights
The wealth of collected experimental data in combination with first-principle results from lattice QCD evidence of the creation of a strongly coupled quantum fluid, the quark-gluon plasma (QGP), in the ultrarelativistic heavyion collisions at the large hadron collider (LHC) and the relativistic heavy ion collider (RHIC) [1,2,3]
We study the temperature dependence of the shear viscosity to entropy density ratio in pure Yang-Mills theory and in QCD with light and strange quarks within kinetic theory in the relaxation time approximation
For pure Yang-Mills theory, we show that the shear viscosity to entropy density ratio exhibits a characteristic nonmonotonicity with a minimum at the firstorder phase transition
Summary
The wealth of collected experimental data in combination with first-principle results from lattice QCD evidence of the creation of a strongly coupled quantum fluid, the quark-gluon plasma (QGP), in the ultrarelativistic heavyion collisions at the large hadron collider (LHC) and the relativistic heavy ion collider (RHIC) [1,2,3]. The QPM was extended by including a finite (and even large) collisional width Γ in the quasiparticle spectral functions With this approach [60,61,62], using the Kubo formalism or kinetic theory with relaxation times τ 1⁄4 1=Γ, an η=s similar to the first-principle and fluid dynamical simulation results was obtained. We study the temperature dependence of the specific shear viscosity of deconfined strongly interacting matter for pure Yang-Mills theory and for matter antimatter symmetric QCD with Nf 1⁄4 2 þ 1 quark flavors Both systems are described in a framework with quasiparticle d.o.f. The shear viscosity is calculated from kinetic theory in the relaxation time approximation.
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