The N_f^3 g^6 term in the pressure of hot QCD

We determine the first independent part of the g^6 coefficient in the weak coupling expansion of the QCD pressure at high temperatures, the one proportional to the maximal power of the number of quark flavors N_f. In addition to introducing and developing computational methods that can be used in evaluating other parts of the expansion, our calculation provides a result that becomes dominant in the limit of large N_f and a fixed effective coupling g_{eff}^2 = g^2 N_f/2.Comment: 9 pages, 2 figures, revtex, v2: minor modifications and additional reference

Dimensional reduction and the phase diagram of 5d Yang-Mills theory

We present a non-perturbative study of the phase diagram of 5d SU(2) Yang-Mills theory with one compact extra dimension on the lattice. Assuming at least a modest scale separation between the cutoff and the compactification scales leads to an exponential separation between the compactification scale and the four-dimensional correlation length. While we demonstrate that it is not possible to take a full five-dimensional continuum limit, this dynamical generation of scale hierarchy opens up the possibility for us to make limited, but non-perturbative, predictions about continuum theories whose low-energy sector is described by an effective 5d Yang-Mills theory.Comment: 7 pages. Presented at the XXVII International Symposium on Lattice Field Theory, July 26-31, 2009, Peking University, Beijing, Chin

Framework for non-perturbative analysis of a Z(3)-symmetric effective theory of finite temperature QCD

We study a three dimensional Z(3)-symmetric effective theory of high temperature QCD. The exact lattice-continuum relations, needed in order to perform lattice simulations with physical parameters, are computed to order O(a^0) in lattice perturbation theory. Lattice simulations are performed to determine the phase structure of a subset of the parameter space.Comment: 28 pages, 11 figures; v3: references rearranged, typos corrected, figs changed, published versio

EMMI Rapid Reaction Task Force on "Thermalization in Non-abelian Plasmas"

Recently, different proposals have been put forward on how thermalization proceeds in heavy-ion collisions in the idealized limit of very large nuclei at sufficiently high energy. Important aspects of the parametric estimates at weak coupling may be tested using well-established classical-statistical lattice simulations of the far-from-equilibrium gluon dynamics. This has to be confronted with strong coupling scenarios in related theories based on gauge-string dualities. Furthermore, closely related questions about far-from-equilibrium dynamics arise in early-universe cosmology and in non-relativistic systems of ultracold atoms. These were central topics of the EMMI Rapid Reaction Task Force meeting held on December 12-14, 2011, at the University of Heidelberg, which we report on.Comment: 13 pages, summary of the EMMI Rapid Reaction Task Force on "Thermalization in Non-abelian Plasmas", December 12-14, 2011, University of Heidelberg, German

Heavy quark momentum diffusion coefficient in 3D gluon plasma

We study the heavy-quark momentum diffusion coefficient in far from equilibrium gluon plasma in a self-similar regime using real-time lattice techniques. We use 3 methods for the extraction: an unequal time electric field 2-point correlator integrated over the time difference, a spectral reconstruction (SR) method based on the measured equal time electric field correlator and a kinetic theory (KT) formula. The time-evolution of the momentum diffusion coefficient extracted using all methods is consistent with an approximate t(-1/2) power law. We also study the extracted diffusion coefficient as a function of the upper limit of the time integration and observe that including the infrared enhancement of the equal-time correlation function in the SR calculation improves the agreement with the data for transient time behavior considerably. This is a gauge invariant confirmation of the infrared enhancement previously observed only in gauge fixed correlation functions.Peer reviewe

Cold Quark Matter

We perform an O(alpha_s^2) perturbative calculation of the equation of state of cold but dense QCD matter with two massless and one massive quark flavor, finding that perturbation theory converges reasonably well for quark chemical potentials above 1 GeV. Using a running coupling constant and strange quark mass, and allowing for further non-perturbative effects, our results point to a narrow range where absolutely stable strange quark matter may exist. Absent stable strange quark matter, our findings suggest that quark matter in compact star cores becomes confined to hadrons only slightly above the density of atomic nuclei. Finally, we show that equations of state including quark matter lead to hybrid star masses up to M~2M_solar, in agreement with current observations. For strange stars, we find maximal masses of M~2.75M_solar and conclude that confirmed observations of compact stars with M>2M_solar would strongly favor the existence of stable strange quark matter.Comment: 51 pages, 11 figures, v2: minor modifications and additional reference

Spectral function for overoccupied gluodynamics from real-time lattice simulations

We study the spectral properties of a highly occupied non-Abelian nonequilibrium plasma appearing ubiquitously in weak coupling descriptions of QCD matter. The spectral function of this far-from-equilibrium plasma is measured by employing linear response theory in classical-statistical real-time lattice Yang-Mills simulations. We establish the existence of transversely and longitudinally polarized quasi-particles and obtain their dispersion relations, effective mass, plasmon frequency, damping rate and further structures in the spectral and statistical functions. Our new method can be interpreted as a nonperturbative generalization of hard thermal loop (HTL) effective theory. We see indications that our results approach leading order HTL in the appropriate limit. The method can also be employed beyond the range of validity of HTL.Peer reviewe

Heavy quark diffusion in an overoccupied gluon plasma

We extract the heavy-quark diffusion coefficient kappa and the resulting momentum broadening in a far-from-equilibrium non-Abelian plasma. We find several features in the time dependence of the momentum broadening: a short initial rapid growth of , followed by linear growth with time due to Langevin-type dynamics and damped oscillations around this growth at the plasmon frequency. We show that these novel oscillations are not easily explained using perturbative techniques but result from an excess of gluons at low momenta. These oscillation are therefore a gauge invariant confirmation of the infrared enhancement we had previously observed in gauge-fixed correlation functions. We argue that the kinetic theory description of such systems becomes less reliable in the presence of this IR enhancement.Peer reviewe

SPECTRAL FUNCTION FOR OVEROCCUPIED GLUODYNAMICS FROM CLASSICAL LATTICE SIMULATIONS

We study the spectral properties of an overoccupied gluonic system far from equilibrium. Using classical Yang-Mills simulations and linear response theory, we determine the statistical and spectral functions. We measure dispersion relations and damping rates of transversally and longitudinally polarized excitations in the gluonic plasma, and also study further structures in the spectral function.Peer reviewe

Plaquette expectation value and lattice free energy of three-dimensional SU(N) gauge theory

We use high precision lattice simulations to calculate the plaquette expectation value in three-dimensional SU(N) gauge theory for N=2,3,4,5,8. Using these results, we study the N-dependence of the first non-perturbative coefficient in the weak-coupling expansion of hot QCD. We demonstrate that, in the limit of large N, the functional form of the plaquette expectation value with ultraviolet divergences subtracted is 15.9(2)-44(2)/N^2.Comment: 14 pages, 6 figures. v2: references added; published versio