{"arxiv_id":"1212.5393","title":"Shear and bulk viscosities of strongly-interacting 'infinite' parton-hadron matter within the parton-hadron-string transport approach","abstract":"We study the shear and bulk viscosities of partonic and hadronic matter as functions of temperature T within the parton-hadron-string dynamics (PHSD) off-shell transport approach. Dynamical hadronic and partonic systems in equilibrium are studied by the PHSD simulations in a finite box with periodic boundary conditions. The ratio of the shear viscosity to entropy density \\eta(T)/s(T) from PHSD shows a minimum (with a value of about 0.1) close to the critical temperature T_c, while it approaches the perturbative QCD limit at higher temperatures in line with lattice QCD (lQCD) results. For T<T_c, i.e., in the hadronic phase, the ratio \\eta/s rises fast with decreasing temperature due to a strong decrease of the entropy density $s$ in the hadronic phase at decreasing T. Within statistics, we obtain practically the same results in the Kubo formalism and in the relaxation time approximation. The bulk viscosity \\zeta(T)---evaluated in the relaxation time approach---is found to strongly depend on the effects of mean fields (or potentials) in the partonic phase. We find a significant rise of the ratio \\zeta(T)/s(T) in the vicinity of the critical temperature T_c, when consistently including the scalar mean-field from PHSD, which is also in agreement with that from lQCD calculations. Furthermore, we present the results for the ratio (\\eta+ 3\\zeta/4)/s, which is found to depend nontrivially on temperature and to generally agree with the lQCD calculations as well. Within the PHSD calculations, the strong maximum of \\zeta(T)/\\eta(T) close to T_c has to be attributed to mean-field (or potential) effects that in PHSD are encoded in the temperature dependence of the quasiparticle masses, which is related to the infrared enhancement of the resummed (effective) coupling g(T).","primary_cat":"hep-ph","cross_cats":["nucl-th"],"submitted_at":"2012-12-21T10:55:42+00:00","latest_version":2,"source":"arxiv","source_label":"arXiv","source_url":null,"has_pdf":true,"has_source":false,"verdict":"CONDITIONAL","confidence":"MODERATE","one_line_summary":"The PHSD transport model reproduces the temperature dependence of shear and bulk viscosity of strongly interacting matter, including a mean-field-driven bulk-viscosity peak near the critical temperature.","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","upvotes":0,"downvotes":0,"pith_score":0,"inbound_count":11,"_links":{"html":"https://pith.science/paper/1212.5393","verdict":"/api/v1/verdicts/1212.5393"}}