We present results for pseudo-critical temperatures of QCD chiral crossovers at zero and non-zero values of baryon (B), strangeness (S), electric charge (Q), and isospin (I) chemical potentials µ X=B,Q,S,I . The results were obtained using lattice QCD calculations carried out with two degenerate up and down dynamical quarks and a dynamical strange quark, with quark masses corresponding to physical values of pion and kaon masses in the continuum limit. By parameterizing pseudo-critical temperatures as (0)) 4 , we determined κ X 2 and κ X 4 from Taylor expansions of chiral observables in µ X . We obtained a precise result for T c (0) = (156.5 ± 1.5) MeV. For analogous thermal conditions at the chemical freeze-out of relativistic heavy-ion collisions, i.e., µ S (T, µ B ) and µ Q (T, µ B ) fixed from strangeness-neutrality and isospin-imbalance, we found κ B 2 =0.012(4) and κ B 4 =0.000(4). For µ B 300 MeV, the chemical freeze-out takes place in the vicinity of the QCD phase boundary, which coincides with the lines of constant energy density of 0.42(6) GeV/fm 3 and constant entropy density of 3.7(5) fm −3 .

HotQCD Collaboration)We present a lattice-QCD-based determination of the chiral phase transition temperature in QCD with two degenerate, massless quarks and a physical strange quark mass using lattice QCD calculations with the Highly Improved Staggered Quarks action. We propose and calculate two novel estimators for the chiral transition temperature for several values of the light quark masses, corresponding to Goldstone pion masses in the range of 58 MeV < ∼ mπ < ∼ 163 MeV. The chiral phase transition temperature is determined by extrapolating to vanishing pion mass using universal scaling analysis. Finite-volume effects are controlled by extrapolating to the thermodynamic limit using spatial lattice extents in the range of 2.8-4.5 times the inverse of the pion mass. Continuum extrapolations are carried out by using three different values of the lattice cutoff, corresponding to lattices with temporal extents Nτ = 6, 8 and 12. After thermodynamic, continuum, and chiral extrapolations we find the chiral phase transition temperature T 0 c = 132 +3 −6 MeV.Introduction.-For physical values of the light up, down, and heavier strange quark masses strongly interacting matter undergoes a transition from a lowtemperature hadronic regime to a high-temperature region that is best described by quark and gluon degrees of freedom. This smooth crossover between the two asymptotic regimes is not a phase transition [1]. It is characterized by a pseudocritical temperature, T pc , that has been determined in several numerical studies of Quantum Chromodynamics (QCD) [2][3][4]. A recent determination of T pc extracted from the maximal fluctuations of several chiral observables gave T pc = (156.5 ± 1.5) MeV [5].

We present lattice QCD results for mesonic screening masses in the temperature range 140 MeV T 2500 MeV. Our calculations were carried out using (2+1)-flavors of the Highly Improved Staggered Quark (HISQ) action, with a physical value for the strange quark mass and two values of the light quark mass corresponding to pion masses of 160 MeV and 140 MeV. Continuumextrapolated results were obtained using calculations with a variety of lattice spacings corresponding to temporal lattice extents Nτ = 6 -16. We discuss the implications of these results for the effective restoration of various symmetries in the high temperature phase of QCD, as well as the approach toward the perturbative limit.

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We have calculated the shear viscosity coefficient η of the strongly interacting matter in the relaxation time approximation, where a quasiparticle description of quarks with their dynamical masses is considered from the Nambu-Jona-Lasinio model. Due to the thermodynamic scattering of quarks with pseudoscalar-type condensate (i.e., pion), a nonzero Landau damping will be acquired by the propagating quarks. This Landau damping may be obtained from the Landau cut contribution of the in-medium self-energy of a quark-pion loop, which is evaluated in the framework of real-time thermal field theory. From the basic idea of the QCD asymptotic freedom at high temperatures and densities, a weakly interacting quark gluon plasma (QGP) is naturally expected to be produced in heavy ion collision (HIC) experiments. However, the experimental data from the BNL Relativistic Heavy Ion Collider (RHIC), especially the measured elliptic flow, indicate that nuclear matter is a strongly interacting liquid instead of a weakly interacting gas. The recent hydrodynamical calculations [1,2] as well as some calculations of kinetic transport theory [3,4] conclude that the matter produced in a HIC must have very small shear viscosity. The shear viscosity of the fluid is generally quantified by the the coefficient η and it physically interprets the ability to transfer momentum over a distance of the mean free path. Hence the lower values of η means the constituents of the matter interact strongly to transfer the momentum easily. Whereas a weakly interacting system must have large η because in this case the momentum transfer between the constituents becomes strenuous.Several theoretical attempts have been taken to calculate the η of the strongly interacting matter at very high [5], intermediate [6,7], and low [8][9][10][11][12][13][14][15][16] temperatures, where some special attention was drawn to the smallness of its original value with respect to its lower bound (η =s 4π, where s is the entropy density), commonly known as the KSS bound [26]. A most interesting fact, which has been added with the recent theoretical understanding of η for strongly interacting matter, is that the η/s may reach a minimum in the vicinity of a phase transition [19][20][21][22][23] (see also [27]) like the liquid-gas phase transition of certain materials, e.g., nitrogen, helium, or water. These investigations demand a better understanding to zoom in on the temperature T dependence of η of the strongly interacting matter near the phase transition. Inspired by this motivation, in this Brief Report we have addressed the η(T ) due to forward and backward scattering of the quark-pion interaction.In the relaxation time approximation, the η of the quark [23] and pion [15,16] medium (for μ = 0) can be expressed aswhereand n π = 1 e βωπ −1 are, respectively, the Fermi-Dirac distribution of the quark and the Bose-Einstein distribution of the pion withπ . The Q and π are Landau damping of the quark and pion, respectively. Following the quasiparticle description of the Nambu-J...