Thermalization and plasma instabilities

I review recent analytical and numerical advances in the study of non-equilibrium quark-gluon plasma physics. I concentrate on studies of the dynamics of plasmas which are locally anisotropic in momentum space. In contrast to locally isotropic plasmas such anisotropic plasmas have a spectrum of soft unstable modes which are characterized by exponential growth of transverse (chromo)-magnetic fields at short times. Parametrically the instabilities provide the fastest method for generation of soft background fields and dominate the short-time dynamics of the system.Comment: 8 pages, 3 figures; Contribution to the proceedings of the International Conference on Strong & Electroweak Matter 2006, Brookhaven National Laboratory, Upton, NY, May 200

Viscosity Information from Relativistic Nuclear Collisions: How Perfect is the Fluid Observed at RHIC?

Relativistic viscous hydrodynamic fits to RHIC data on the centrality dependence of multiplicity, transverse and elliptic flow for sqrt{s}=200 GeV Au+Au collisions are presented. For Glauber-type initial conditions, while data on integrated v_2 is consistent with a ratio of viscosity over entropy density up to eta/s=0.16, data on minimum bias v_2 seems to favor a much smaller viscosity over entropy ratio, below the bound from the AdS/CFT conjecture. Some caveats on this result are discussed.Comment: 4 pages, 5 figures; v2: matches published version, title changed by journa

A Weibel Instability in the Melting Color Glass Condensate

Based on hep-ph/0510121, we discuss further the numerical study of classical SU(2) 3+1-D Yang-Mills equations for matter produced in a high energy heavy ion collision. The growth of the amplitude of fluctuations as $\exp{(\Gamma \sqrt{g^2\mu \tau})}$ (where $g^2\mu$ is a scale arising from the saturation of gluons in the nuclear wavefunction) is shown to be robust over a wide range of initial amplitudes that violate boost invariance. We argue that this growth is due to a non-Abelian Weibel instability, the scale of which is set by a dynamically generated plasmon mass. We find good agreement when we relate $\Gamma$ to the prediction from kinetic theory.Comment: 8 pages, invited talk at Workshop on Quark Gluon Plasma Thermalization, Vienna, August 10th-12th, 200

Do nuclear collisions create a locally equilibrated quark-gluon plasma?

Experimental results on azimuthal correlations in high energy nuclear collisions (nucleus-nucleus, proton-nucleus and proton-proton) seem to be well described by viscous hydrodynamics. It is often argued that this agreement implies either local thermal equilibrium or at least local isotropy. In this note, I present arguments why this is not the case. Neither local near-equilibrium nor near-isotropy are required in order for hydrodynamics to offer a successful and accurate description of experimental results. However, I predict the breakdown of hydrodynamics at momenta of order seven times the temperature, corresponding to a smallest possible QCD liquid drop size of 0.15 fm.Comment: 14 pages, 6 figures; v2: references added, major changes in section VI, qualitative conclusions unchanged; v3: minor typos fixed, matches published versio

Cold deconfined matter EOS through an HTL quasi-particle model

Using quasi-particle models, lattice data can be mapped to finite chemical potential. By comparing a simple and an HTL quasi-particle model, we derive the general trend that a full inclusion of the plasmon effect will give.Comment: 5 pages, 6 figures, contribution to the conference Strong and Electroweak Matter (SEWM2002), Heidelberg, Germany, October 2-5, 2002; v2: plots and references update

Relativistic Hydrodynamic Attractors with Broken Symmetries: Non-Conformal and Non-Homogeneous

Standard textbooks will state that hydrodynamics requires near-equilibrium to be applicable. Recently, however, out-of-equilibrium attractor solutions for hydrodynamics have been found in kinetic theory and holography in systems with a high degree of symmetry, suggesting the possibility of a genuine out-of-equilibrium formulation of hydrodynamics. This work demonstrates that attractor solutions also occur in non-conformal kinetic theory and spatially non-homogeneous systems, potentially having important implications for the interpretation of experimental data in heavy-ion and proton-proton collisions and relativistic fluid dynamics as a whole.Comment: 13 pages, 2 figures; v2: minor changes (typos, etc.); v3: matches published versio