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Register a new userShear viscosity and electric conductivity of a hot and dense QGP with a chiral phase transition
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We calculate two transport coefficients -- the shear viscosity over entropy ratio $eta/s$ and the ratio of the electric conductivity to the temperature $sigma_0/T$ -- of strongly interacting quark matter within the extended $N_f=3$ Polyakov Nambu-Jona-Lasinio (PNJL) model along the crossover transition line for moderate values of baryon chemical potential $0 leq mu_B leq 0.9$ GeV as well as in the vicinity of the critical endpoint (CEP) and at large baryon chemical potential $mu_B=1.2$ GeV, where the first-order phase transition takes place. The evaluation of the transport coefficients is performed on the basis of the effective Boltzmann equation in the relaxation time approximation. We employ two different methods for the calculation of the quark relaxation times: i) using the averaged transition rate defined via thermal averaged quark-quark and quark-antiquark PNJL cross sections and ii) using the weighted thermal averaged quark-quark and quark-antiquark PNJL cross sections. The $eta/s$ and $sigma_0/T$ transport coefficients have a similar temperature and chemical potential behavior when approaching the chiral phase transition for the both methods for the quark relaxation time, however, the differences grow with increasing temperature. We demonstrate the effect of the first-order phase transition and of the CEP on the transport coefficients in the deconfined QCD medium.
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The electric conductivity is considered in the fully anisotropic holographic theory. The electric conductivity is derived in two different ways, and their equivalence for the fully anisotropic theory is shown. Numerical calculations of the electric conductivity were done for Einstein-dilaton-three-Maxwell holographic model [29]. The dependence of the conductivity on the temperature, the chemical potential, the external magnetic field, and the spatial anisotropy of the heavy-ions collision (HIC) is studied. The electric conductivity jumps near the first-order phase transition are observed. This effect is similar to the jumps of holographic entanglement that were studied previously.
The Color String Percolation Model (CSPM) is used to determine the shear viscosity to entropy ratio ($eta/s$) of the Quark-Gluon Plasma (QGP) produced in Au-Au collisions at $sqrt{s_{NN}}$ = 200 GeV at RHIC and Pb-Pb at $sqrt{s_{NN}}$ = 2.76 TeV at LHC. The relativistic kinetic theory relation for $eta/s$ is evaluated using CSPM values for the temperature and the mean free path of the QGP constituents. The experimental charged hadron transverse momentum spectrum is used to determine the percolation density parameter $xi$ in Au-Au collisions (STAR). For Pb-Pb at $sqrt{s_{NN}}$ = 2.76 TeV $xi$ values are obtained from the extrapolation at RHIC energy. The value of $eta/s$ is 0.204$pm$0.020 and 0.262$pm$0.026 at the CSPM initial temperatures of 193.6$pm$3 MeV (RHIC) and 262.2 $pm$13 MeV (LHC) respectively. These values are 2.5 and 3.3 times the AdS/CFT conjectured lower bound $1/4pi$. We compare the CSPM $eta/s$ analytic expression with weak coupling (wQGP) and strong coupling (sQGP) calculations. This indicates that the QGP is a strongly coupled fluid in the phase transition region.
We have studied the collisional time and relaxation time of a QGP(Quark-Gluon Plasma) by parameterizing them by temperature. From this parameterization we have obtained the decay rate parameterized by temperature which further helps us to calculate and compare the shear viscosity to entropy density ratio of a QGP with the KSS(Kovtun-Son-Starinets) result.
Motivated by the existence of unstable modes of compact stars that eventually grow large, we study the bulk viscosity of dense matter, taking into account non-linear effects arising in the large amplitude regime, where the deviation mu_Delta of the chemical potentials from chemical equilibrium fulfills mu_Delta > T. We find that this supra-thermal bulk viscosity can provide a potential mechanism for saturating unstable modes in compact stars since the viscosity is strongly enhanced. Our study confirms previous results on strange quark matter and shows that the suprathermal enhancement is even stronger in the case of hadronic matter. We also comment on the competition of different weak channels and the presence of suprathermal effects in various color superconducting phases of dense quark matter.
We present calculations for the shear viscosity of the hot and dense quark-gluon plasma (QGP) using the partonic scattering cross sections as a function of temperature $T$ and baryon chemical potential $mu_B$ from the dynamical quasiparticle model (DQPM) that is matched to reproduce the equation of state of the partonic system above the deconfinement temperature $T_c$ from lattice QCD. To this aim we calculate the collisional widths for the partonic degrees of freedom at finite $T$ and $mu_B$ in the time-like sector and conclude that the quasiparticle limit holds sufficiently well. Furthermore, the ratio of shear viscosity $eta$ over entropy density $s$, i.e. $eta/s$, is evaluated using these collisional widths and are compared to lQCD calculations for $mu_B$ = 0 as well. We find that the ratio $eta/s$ is in agreement with the results of calculations within the original DQPM on the basis of the Kubo formalism. Furthermore, there is only a very modest change of $eta/s$ with the baryon chemical $mu_B$ as a function of the scaled temperature $T/T_c(mu_B)$.
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