nucl-th digest · Dec 10, 2014

Hydrodynamic transport coefficients for the non-conformal quark-gluon plasma from holography

In this paper we obtain holographic formulas for the transport coefficients

κ

and

τ_{π}

present in the second-order derivative expansion of relativistic hydrodynamics in curved spacetime associated with a non-conformal strongly coupled plasma described holographically by an Einstein+Scalar action in the bulk. We compute these coefficients as functions of the temperature in a bottom-up non-conformal model that is tuned to reproduce lattice QCD thermodynamics at zero baryon chemical potential. We directly compute, besides the speed of sound, 6 other transport coefficients that appear at second-order in the derivative expansion. We also give an estimate for the temperature dependence of 11 other transport coefficients taking into account the simplest contribution from non-conformal effects that appear near the QCD crossover phase transition. Using these results, we construct an Israel-Stewart-like theory in flat spacetime containing 13 of these 17 transport coefficients that should be suitable for phenomenological applications in the context of numerical hydrodynamic simulations of the strongly-coupled, non-conformal quark-gluon plasma. Using several different approximations, we give parametrizations for the temperature dependence of all the second-order transport coefficients that appear in this theory in a format that can be easily implemented in existing numerical hydrodynamic codes.

↳ hep-phhep-thnucl-thJHEP(2015)·145 citations

Dynamical Generation of a Repulsive Vector Contribution to the Quark Pressure

Tulio E. Restrepo🇧🇷 · Juan Camilo Macias🇧🇷 · Marcus Benghi Pinto🇧🇷 · Gabriel N. Ferrari🇧🇷

Lattice QCD results for the coefficient $c_{2}$ appearing in the Taylor expansion of the pressure show that this quantity raises with the temperature towards the Stefan-Boltzmann limit. On the other hand, model approximations predict that when a vector repulsion, parametrized by $G_{V}$ , is present this coefficient reaches a maximum just after $T_{c}$ and then deviates from the lattice predictions. Recently, this discrepancy has been used as a guide to constrain the (presently unknown) value of $G_{V}$ within the framework of effective models at large- $N_{c}$ (LN). In the present investigation we show that, due to finite $N_{c}$ effects, $c_{2}$ may also develop a maximum even when $G_{V} = 0$ since a vector repulsive term can be dynamically generated by exchange type of radiative corrections. Here we apply the the Optimized Perturbation Theory (OPT) method to the two flavor Polyakov--Nambu--Jona-Lasinio model (at $G_{V} = 0$ ) and compare the results with those furnished by lattice simulations an by the LN approximation at $G_{V} = 0$ and also at $G_{V} \neq = 0$ . The OPT numerical results for $c_{2}$ are impressively accurate for $T ≲ 1.2 T_{c}$ but, as expected, predict that this quantity develops a maximum at high- $T$ . After identifying the mathematical origin of this extremum we argue that such a discrepant behavior may naturally arise within these effective quark models (at $G_{V} = 0$ ) whenever the first $1/ N_{c}$ corrections are taken into account. We then interpret this hypothesis as an indication that beyond the large- $N_{c}$ limit the correct high temperature (perturbative) behavior of $c_{2}$ will be faithfully described by effective models only if they also mimic the asymptotic freedom phenomenon.

↳ hep-phnucl-thPRD(2015)·36 citations

Wednesday·December 10, 2014

Hydrodynamic transport coefficients for the non-conformal quark-gluon plasma from holography

Dynamical Generation of a Repulsive Vector Contribution to the Quark Pressure

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