Direct determination of the gauge coupling derivatives for the energy density in lattice QCD

By matching Wilson loop ratios on anisotropic lattices we measure the coefficients \cs and \ct, which are required for the calculation of the energy density. The results are compared to that of an indirect method of determination. We find similar behaviour, the differences are attributed to different discretization errors.Comment: Talk presented at LATTICE97(finite temperature), 3 pages, 5 Postscript figure

Cutoff effects in meson spectral functions

We study the lattice spacing dependence of meson spectral functions calculated in quenched QCD with domain wall fermions as well as clover Wilson fermions in quenched and partially-quenched QCD. We conclude that for lattice spacing $a \le 3$ GeV all excited states appearing in the spectral functions are lattice artifacts.Comment: Lattice 2004 (non-zero), 3 pages, 3 figures, uses espcrc2 packag

Infrared features of unquenched finite temperature lattice Landau gauge QCD

The color diagonal and color antisymmetric ghost propagators slightly above $T_c$ of $N_f=2$ MILC $24^3\times 12$ lattices are measured and compared with zero temperature unquenched $N_f=2+1$ MILC$_c$ $20^3\times 64$ and MILC$_f$ $28^3\times 96$ lattices and zero temperature quenched $56^4$ $\beta=6.4$ and 6.45 lattices. The expectation value of the color antisymmetric ghost propagator $\phi^c(q)$ is zero but its Binder cumulant, which is consistent with that of $N_c^2-1$ dimensional Gaussian distribution below $T_c$, decreases above $T_c$. Although the color diagonal ghost propagator is temperature independent, the $l^1$ norm of the color antisymmetric ghost propagator is temperature dependent. The expectation value of the ghost condensate observed at zero temperature unquenched configuration is consistent with 0 in $T>T_c$. We also measure transverse, magnetic and electric gluon propagator and extract gluon screening masses. The running coupling measured from the product of the gluon dressing function and the ghost dressing function are almost temperature independent but the effect of $A^2$ condensate observed at zero temperature is consistent with 0 in $T>T_c$. The transverse gluon dressing function at low temperature has a peak in the infrared but it becomes flatter at high temperature. Its absolute value in the high momentum is larger for high temperature and similar to the magnetic gluon dressing function. The electric gluon propagator at high momentum is temperature independent. These data imply that the magnetic gluon propagator and the color antisymmetric ghost propagator are affected by the presence of dynamical quarks and there are strong non-perturbative effects through the temperature dependent color anti-symmetric ghost propagator.Comment: 11 pages 16 figures, version accepted for publication in Phys. Rev.

Probing the QCD Equation of State

We propose a novel quasiparticle interpretation of the equation of state of deconfined QCD at finite temperature. Using appropriate thermal masses, we introduce a phenomenological parametrisation of the onset of confinement in the vicinity of the phase transition. Lattice results of bulk thermodynamic quantities are well reproduced, the extension to small quark chemical potential is also successful. We then apply the model to dilepton production and charm suppression in ultrarelativistic heavy-ion collisions.Comment: 6 pages, 8 figures. Invited talk presented by R. A. Schneider at the XVI International Conference on Particles and Nuclei (PANIC02), Osaka, Japan, September 30 - October 4, 200

QCD strings and the thermodynamics of the metastable phase of QCD at large NcN_c

The thermodyanmics of a metastable hadronic phase of QCD at large $N_C$ are related to properties of an effective QCD string. In particular, it is shown that in the large $N_c$ limit and near the maximum hadronic temperature, $T_H$, the energy density and pressure of the metastable phase scale as ${\cal E} \sim (T_H-T)^{-(D_\perp-6)/2}$ (for $D_\perp <6$) and $P \sim (T_H-T)^{-(D_\perp-4)/2}$ (for $D_\perp <4$) where $D_\perp$ is the effective number of transverse dimensions of the string theory. It is shown, however, that for the thermodynamic quantities of interest the limits $T \to T_H$ and $N_c \to \infty$ do not commute. The prospect of extracting $D_\perp$ via lattice simulations of the metastable hadronic phase at moderately large $N_c$ is discussed.Comment: After this paper was published, the author became aware of an important early paper by Charles Thorn on the subject of the QCD phase transition at large N_c and its relation to the Hagedorn spectrum. Given the pioneering nature of Thorn's paper, and the fact that it is not as widely known as it should be, it is important to cite it in the present work. This updated version cites Thorn's wor

The boundary of the first order chiral phase transition in the m_pi-m_K--plane with a linear sigma model

Tree-level and complete one-loop parametrisation of the linear sigma model (LSM) is performed and the phase boundary between first order and crossover transition regions of the m_pi-m_K-plane is determined using the optimised perturbation theory (OPT) as a resummation tool of perturbative series. Away from the physical point the parameters of the model were determined by making use of chiral perturbation theory (ChPT). The location of the phase boundary for m_pi=m_K and of the tricritical point (TCP) on the m_pi=0 were estimated.Comment: 4 pages, 1 figure, uses espcrc1.sty; to appear in the proceedings of Strong and Electroweak Matter 2006 (SEWM06), BNL, May 200

Anisotropic Lattices and Dynamical Fermions

We report results from full QCD calculations with two flavors of dynamical staggered fermions on anisotropic lattices. The physical anisotropy as determined from spatial and temporal masses, their corresponding dispersion relations, and spatial and temporal Wilson loops is studied as a function of the bare gauge anisotropy and the bare velocity of light appearing in the Dirac operator. The anisotropy dependence of staggered fermion flavor symmetry breaking is also examined. These results will then be applied to the study of 2-flavor QCD thermodynamics.Comment: Lattice2001(spectrum

A Lower Bound on TSR/mHT_{SR}/{m_{\rm H}} in the O(4) Model on Anisotropic Lattices

Results of an investigation of the $O(4)$ spin model at finite temperature using anisotropic lattices are presented. In both the large $N$ approximation and numerical simulations using the Wolff cluster algorithm we find that the ratio of the symmetry restoration temperature $T_{\rm SR}$ to the Higgs mass $m_{\rm H}$ is independent of the anisotropy $\xi$. From the numerical simulations we obtain a lower bound of $T_{\rm SR} / m_{\rm H} \simeq 0.58 \pm 0.02$ at a value for the Higgs mass $m_{\rm H}a_s \simeq 0.5$, which is lowered further by about $10\%$ at $m_{\rm H}a_s \simeq 1$. Requiring certain timelike correlation functions to coincide with their spacelike counterparts, quantum and scaling corrections to the anisotropy are determined and are found to be small, i.e., the anisotropy is found to be close to the ratio of spacelike and timelike lattice spacings.Comment: 16 pages with 4 ps figures included. LaTeX file. BI-TP 92/27, FSU-SCRI-92-101, HLRZ-92-40, TIFR/TH/92-4

Phase diagram at finite temperature and quark density in the strong coupling limit of lattice QCD for color SU(3)

We study the phase diagram of quark matter at finite temperature (T) and finite chemical potential (mu) in the strong coupling limit of lattice QCD for color SU(3). We derive an analytical expression of the effective free energy as a function of T and mu, including baryon effects. The finite temperature effects are evaluated by integrating over the temporal link variable exactly in the Polyakov gauge with anti-periodic boundary condition for fermions. The obtained phase diagram shows the first order phase transition at low temperatures and the second order phase transition at high temperatures separated by the tri-critical point in the chiral limit. Baryon has effects to reduce the effective free energy and to extend the hadron phase to a larger mu direction at low temperatures.Comment: 18 pages, 10 figure

The scalar glueball spectrum

We discuss scenarios for scalar glueballs using arguments based on sum rules, spectral decomposition, the $\frac{1}{N_c}$ approximation, the scales of the strong interaction and the topology of the flux tubes. We analyze the phenomenological support of those scenarios and their observational implications. Our investigations hint a rich low lying glueball spectrum.Comment: 11 pages: New title, figure, table and a more detailed comparison with experiment