1,183 research outputs found

    Lattice constraints on the thermal photon rate

    Get PDF
    We estimate the photon production rate from an SU(3) plasma at temperatures of about 1.1Tc and 1.3Tc. Lattice results for the vector current correlator at spatial momenta k ~ (2-6)T are extrapolated to the continuum limit and analyzed with the help of a polynomial interpolation for the corresponding spectral function, which vanishes at zero frequency and matches to high-precision perturbative results at large invariant masses. For small invariant masses the interpolation is compared with the NLO weak-coupling result, hydrodynamics, and a holographic model. At vanishing invariant mass we extract the photon rate which for k \gsim 3T is found to be close to the NLO weak-coupling prediction. For k \lsim 2T uncertainties remain large but the photon rate is likely to fall below the NLO prediction, in accordance with the onset of a strongly interacting behaviour characteristic of the hydrodynamic regime.Comment: 20 pages. v2: clarifications adde

    Numerical study of the equation of state for two flavor QCD at finite density

    Full text link
    We discuss the equation of state for 2 flavor QCD at non-zero temperature and density. Derivatives of lnZ\ln Z with respect to quark chemical potential μq\mu_q up to fourth order are calculated, enabling estimates of the pressure, quark number density and associated susceptibilities as functions of μq\mu_q via a Taylor series expansion. It is found that the fluctuations in the quark number density increase in the vicinity of the phase transition temperature and the susceptibilities start to develop a pronounced peak as μq\mu_q is increased. This suggests the presence of a critical endpoint in the (T,μq)(T, \mu_q) plane.Comment: 5 pages, 4 figures, Talk at Confinement 200

    The non-zero baryon number formulation of QCD

    Get PDF
    We discuss the non-zero baryon number formulation of QCD in the quenched limit at finite temperature. This describes the thermodynamics of gluons in the background of static quark sources. Although a sign problem remains in this theory, our simulation results show that it can be handled quite well numerically. The transition region gets shifted to smaller temperatures and the transition region broadens with increasing baryon number. Although the action is in our formulation explicitly Z(3) symmetric the Polyakov loop expectation value becomes non-zero already in the low temperature phase and the heavy quark potential gets screened at non-vanishing number density already this phase.Comment: LATTICE99(Finite Temperature and Density), Latex2e using espcrc2.sty, 3 pages, 7 figure

    QCD at non-zero chemical potential and temperature from the lattice

    Full text link
    A study of QCD at non-zero chemical potential, mu, and temperature, T, is performed using the lattice technique. The transition temperature (between the confined and deconfined phases) is determined as a function of mu and is found to be in agreement with other work. In addition the variation of the pressure and energy density with mu is obtained for small positive mu. These results are of particular relevance for heavy-ion collision experiments.Comment: Invited paper presented at the Joint Workshop on Physics at the Japanese Hadron Facility, March 2002, Adelaide. 10 pages, uses ws-procs9x6.cls style file (provided

    The QCD equation of state for two flavours at non-zero chemical potential

    Full text link
    We present results of a simulation of 2 flavour QCD on a 163×416^3\times4 lattice using p4-improved staggered fermions with bare quark mass m/T=0.4m/T=0.4. Derivatives of the thermodynamic grand canonical partition function Z(V,T,μu,μd)Z(V,T,\mu_u,\mu_d) with respect to chemical potentials μu,d\mu_{u,d} for different quark flavours are calculated up to sixth order, enabling estimates of the pressure and the quark number density as well as the chiral condensate and various susceptibilities as functions of μu,d\mu_{u,d} via Taylor series expansion. Results are compared to high temperature perturbation theory as well as a hadron resonance gas model. We also analyze baryon as well as isospin fluctuations and discuss the relation to the chiral critical point in the QCD phase diagram. We moreover discuss the dependence of the heavy quark free energy on the chemical potential.Comment: 4 pages, 7 figures, talk presented at Quark Matter 2005, Budapes

    Heavy Quarkonia and Quark Drip Lines in Quark-Gluon Plasma

    Get PDF
    Using the potential model and thermodynamical quantities obtained in lattice gauge calculations, we determine the spontaneous dissociation temperatures of color-singlet quarkonia and the `quark drip lines' which separate the region of bound QQˉQ\bar Q states from the unbound region. The dissociation temperatures of J/ψJ/\psi and χb\chi_b in quenched QCD are found to be 1.62TcT_c and 1.18Tc1.18T_c respectively, in good agreement with spectral function analyses. The dissociation temperature of J/ψJ/\psi in full QCD with 2 flavors is found to be 1.42TcT_c. For possible bound quarkonium states with light quarks, the characteristics of the quark drip lines severely limit the stable region close to the phase transition temperature. Bound color-singlet quarkonia with light quarks may exist very near the phase transition temperature if their effective quark mass is of the order of 300-400 MeV and higher.Comment: 8 pages, 2 figures, in LaTex, invited talk presented at the International Conference on Strangeness in Quark Matter, UCLA, March 26-31, 200

    Magnetic Component of Quark-Gluon Plasma

    Full text link
    We describe recent developments of the "magnetic scenario" of sQGP. We show that at T=(0.81.3)TcT=(0.8-1.3)T_c there is a dense plasma of monopoles, capable of supporting metastable flux tubes. Their existence allows to quantitatively explained the non-trivial TT-dependence of the static QˉQ\bar Q Q potential energy calculated on the lattice. By molecular dynamics simulation we derived transport properties (shear viscosity and diffusion constant) and showed that the best liquid is given by most symmetric plasma, with 50%-50% of electric and magnetic charges. The results are close to those of the ``perfect liquid'' observed at RHIC.Comment: Contribution to the 20th International Conference on Nucleus Nucleus Collisions (Quark Matter 2008
    corecore