The QGP shear viscosity -- elusive goal or just around the corner?

Journal of Physics G Nuclear and Particle Physics (Impact Factor: 2.78). 06/2011; 38(12). DOI: 10.1088/0954-3899/38/12/124045
Source: arXiv


With the new viscous hydrodynamic + hadron cascade hybrid code VISHNU, a
rather precise (O(25%)) extraction of the QGP shear viscosity (eta/s)_QGP from
heavy-ion elliptic flow data is possible if the initial eccentricity of the
collision fireball is known with <5% accuracy. At this point, eccentricities
from initial state models differ by up to 20%, leading to an O(100%)
uncertainty for (eta/s)_QGP. It is shown that a simultaneous comparison of
elliptic and triangular flow, v_2 and v_3, puts strong constraints on initial
state models and can largely eliminate the present uncertainty in (eta/s)_QGP.
The variation of the differential elliptic flow v_2(p_T) for identified hadrons
between RHIC and LHC energies provides additional tests of the evolution model.

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    • "Refs. [1] [2] and references therein), its first principles determination has proved notoriously challenging. As lattice QCD is limited to the Euclidean formulation of the theory and weak coupling expansions of transport constants are tedious to perform and display slow convergence [3], much attention has lately shifted to gauge gravity calculations. "
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    ABSTRACT: We determine a next-to-leading order result for the correlator of the shear stress operator in high-temperature Yang-Mills theory. The computation is performed via an ultraviolet expansion, valid in the limit of small distances or large momenta, and the result is used for writing operator product expansions for the Euclidean momentum and coordinate space correlators as well as for the Minkowskian spectral density. In addition, our results enable us to confirm and refine a shear sum rule originally derived by Romatschke, Son and Meyer.
    Journal of High Energy Physics 09/2011; 2011(12). DOI:10.1007/JHEP12(2011)035 · 6.11 Impact Factor
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    ABSTRACT: Over the last decade a fruitful interplay has developed between analyses of strongly coupled non-abelian plasmas via the gauge/string duality and the phenomenology of the quark-gluon plasma created in heavy ion collisions. I review the reasons why the gauge/string duality is not a precision tool for QCD physics at present, with emphasis on conceptual issues. I then argue that, nevertheless, the duality can provide valuable insights at both the quantitive and the qualitative level. I illustrate this with a few examples, and conclude with a brief discussion of future prospects.
    Journal of Physics G Nuclear and Particle Physics 06/2011; 38(12). DOI:10.1088/0954-3899/38/12/124030 · 2.78 Impact Factor
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    ABSTRACT: Using second--order dissipative hydrodynamics coupled self-consistently to the linear $\sigma$ model we study the 2+1 dimensional evolution of the fireball created in Au+Au relativistic collisions. We analyze the influence of the dynamics of the chiral fields on the charged-hadron elliptic flow $v_2$ and on the ratio $v_4/(v_2)^2$ for a temperature-independent as well as for a temperature-dependent viscosity-to-entropy ratio $\eta/s$ calculated from the linearized Boltzmann equation in the relaxation time approximation. We find that $v_2$ is not very sensitive to the coupling of chiral sources to the hydrodynamic evolution, but the temperature dependence of $\eta/s$ plays a much bigger role on this observable. On the other hand, the ratio $v_4/(v_2)^2$ turns out to be much more sensitive than $v_2$ to both the coupling of the chiral sources and the temperature dependence of $\eta/s$.
    Physical Review C 07/2011; 84(4). DOI:10.1103/PhysRevC.84.044904 · 3.73 Impact Factor
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