Dynamical equilibration of strongly interacting “infinite” parton matter within the parton-hadron-string dynamics transport approach

Abstract

We study the kinetic and chemical equilibration in "infinite" parton matter within the partonhadron-string dynamics off-shell transport approach, which is based on a dynamical quasiparticle model (DQPM) for partons matched to reproduce lattice QCD results-including the partonic equation of state-in thermodynamic equilibrium. The "infinite" parton matter is simulated by a system of quarks and gluons within a cubic box with periodic boundary conditions, at various energy densities, initialized out of kinetic and chemical equilibrium. We investigate the approach of the system to equilibrium and the time scales for the equilibration of different observables. We, furthermore, study particle distributions in the strongly interacting quark-gluon plasma (sQGP) including partonic spectral functions, momentum distributions, abundances of the different parton species, and their fluctuations (scaled variance, skewness, and kurtosis) in equilibrium. We also compare the results of the microscopic calculations with the ansatz of the DQPM. It is found that the results of the transport calculations are in equilibrium well matched by the DQPM for quarks and antiquarks, while the gluon spectral function shows a slightly different shape due to the mass dependence of the gluon width generated by the explicit interactions of partons. The time scales for the relaxation of fluctuation observables are found to be shorter than those for the average values. Furthermore, in the local subsystem, a strong change of the fluctuation observables with the size of the local volume is observed. These fluctuations no longer correspond to those of the full system and are reduced to Poissonian distributions when the volume of the local subsystem becomes small.

Estimating transport coefficients in hot and dense quark matter

“…As may be observed, in all these calculations the ratio ζ/s decreases monotonically with temperature. We might mention here that, such a behavior of decreasing bulk viscosity to entropy ratio was also observed in estimations based on PHSD transport codes [36] as well as in the linear sigma model in the large N limit [38]. This is in contrast with results in Refs.…”

“…The ratio, η/s, in the hadronic phase has been estimated using UrQMD transport in Ref. [35] while the bulk and shear viscosity coefficients have been estimated using parton hadron string dynamics(PHSD) transport code within a relaxation time approximation [36]. The rise of bulk viscosity coefficient near the transition temperature has been observed in various effective models like chiral perturbation theory [37], quasiparticle models [23], linear sigma model [25] and the Nambu-Jona-Lasinio model [39].…”

Electric and magnetic response of hot QCD matter

“…the elliptic flow v 2 could quantitatively be well described by ideal hydrodynamics up to transverse momenta of the order of 1.5 GeV/c [9][10][11][12][13][14]. Recent studies of 'QCD matter' in equilibrium -using lattice QCD calculations [15,16] or partonic transport models in a finite box with periodic boundary conditions [17,18] -have demonstrated that the ratio of the shear viscosity to entropy density η/s should * Electronic address: Thorsten.Steinert@theo.physik.uni-giessen.de have a minimum close to the critical temperature T c , similar to atomic and molecular systems [19]. On the other hand, the ratio of the bulk viscosity to the entropy density ζ/s should have a maximum close to T c [18] or might even diverge at T c [20][21][22][23][24].…”

Dilepton and photon production in the presence of a nontrivial Polyakov loop

“…There are various models which can be used to study the region near T c , which we call the "semi" Quark-Gluon Plasma. This includes Parton Hadron String Dynamics [50][51][52][53][54][55], Polyakov loop models [56][57][58], the functional renormalization group [59][60][61][62][63][64][65][66][67][68][69][70], background field methods [71][72][73], and lastly, matrix models [74][75][76][77][78][79][80][81][82][83][84][85].…”