Ioannis Bouras

Relativistic shock waves in viscous gluon matter.

We solve the relativistic Riemann problem in viscous gluon matter employing a microscopic parton cascade. We demonstrate the transition from ideal to viscous shock waves by varying the shear viscosity to entropy density ratio eta/s from zero to infinity. We show that an eta/s ratio larger than 0.2 prevents the development of well-defined shock waves on time scales typical for ultrarelativistic heavy-ion collisions. Comparisons with viscous hydrodynamic calculations confirm our findings.

Investigation of shock waves in the relativistic Riemann problem: A comparison of viscous fluid dynamics to kinetic theory

We solve the relativistic Riemann problem in viscous matter using the relativistic Boltzmann equation and the relativistic causal dissipative fluid-dynamical approach of Israel and Stewart. Comparisons between these two approaches clarify and point out the regime of validity of second-order fluid dynamics in relativistic shock phenomena. The transition from ideal to viscous shocks is demonstrated by varying the shear viscosity to entropy density ratio

Calculation of shear viscosity using Green-Kubo relations within a parton cascade

\ensuremath{\eta}/s

Electric conductivity of the quark-gluon plasma investigated using a perturbative QCD based parton cascade

. We also find that a good agreement between these two approaches requires a Knudsen number

Relativistic lattice Boltzmann method for quark gluon plasma simulations

\text{Kn}l1/2

Transition from ideal to viscous Mach cones in a kinetic transport approach

.

Relativistic shock waves and mach cones in viscous gluon matter

The shear viscosity of a gluon gas is calculated using the Green-Kubo relation. Time correlations of the energy-momentum tensor in thermal equilibrium are extracted from microscopic simulations using a parton cascade solving various Boltzmann collision processes. We nd that the pQCD based gluon bremsstrahlung described by Gunion-Bertsch processes signicantly lowers the shear viscosity by a factor of 3 8 compared to elastic scatterings. The shear viscosity scales with the coupling as 1=( 2 log(1= s)). For constant s the shear viscosity to entropy density ratio =s has no dependence on temperature. Replacing the pQCD-based collision angle distribution of binary scatterings by an isotropic form decreases the shear viscosity by a factor of 3.

Development of relativistic shock waves in viscous gluon matter

Electric conductivity is sensitive to effective cross sections among the particles of the partonic medium. We investigate the electric conductivity of a hot plasma of quarks and gluons, solving the relativistic Boltzmann equation. In order to extract this transport coefficient, we employ the Green-Kubo formalism and, independently, a method motivated by the classical definition of electric conductivity. To this end we evaluate the static electric diffusion current upon the influence of an electric field. Both methods give identical results. For the first time, we obtain numerically the Drude electric conductivity formula for an ultrarelativistic gas of quarks and gluons employing constant isotropic binary cross sections. Furthermore, we extract the electric conductivity for a system of massless quarks and gluons including screened binary and inelastic, radiative 2

Heat conductivity in relativistic systems investigated using a partonic cascade

3 perturbative QCD scattering. Comparing with recent lattice results, we find an agreement in the temperature dependence of the conductivity.

Mach cones in viscous heavy-ion collisions

(Dated: September 13, 2011)In this paper, we investigate the recently developed lattice Boltzmann model for relativistic hydro-dynamics. To this purpose, we perform simulations of shock waves in quark-gluon plasma in the lowand high viscosities regime, using three different computational models, the relativistic lattice Boltz-mann (RLB), the Boltzmann Approach Multi-Parton Scattering (BAMPS), and the viscous sharpand smooth transport algorithm (vSHASTA). From the results, we conclude that the RLB modeldeparts from BAMPS in the case of high speeds and high temperature(viscosities), the departurebeing due to the fact that the RLB is based on a quadratic approximation of the Maxwell-Ju¨ttnerdistribution, which is only valid for sufficiently low temperature and velocity. Furthermore, we haveinvestigated the influence of the lattice speed on the results, and shown that inclusion of quadraticterms in the equilibrium distribution improves the stability of the method within its domain ofapplicability. Finally, we assess the viability of the RLB model in the various parameter regimesrelevant to ultra-relativistic fluid dynamics.