QCD Thermodynamics with Improved Actions

The thermodynamics of the SU(3) gauge theory has been analyzed with tree level and tadpole improved Symanzik actions. A comparison with the continuum extrapolated results for the standard Wilson action shows that improved actions lead to a drastic reduction of finite cut-off effects already on lattices with temporal extent $N_\tau=4$. Results for the pressure, the critical temperature, surface tension and latent heat are presented. First results for the thermodynamics of four-flavour QCD with an improved staggered action are also presented. They indicate similarly large improvement factors for bulk thermodynamics.Comment: Talk presented at LATTICE96(finite temperature) 4 pages, LaTeX2e file, 6 eps-file

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

Thermodynamics of Four-Flavour QCD with Improved Staggered Fermions

We have calculated the pressure and energy density in four-flavour QCD using improved fermion and gauge actions. We observe a strong reduction of finite cut-off effects in the high temperature regime, similar to what has been noted before for the SU(3) gauge theory. Calculations have been performed on $16^3\times 4$ and 16^4 lattices for two values of the quark mass, $ma = 0.05$ and 0.1. A calculation of the string tension at zero temperature yields a critical temperature $T_c/\sqrt{\sigma} = 0.407 \pm 0.010$ for the smaller quark mass value.Comment: 12 pages, LaTeX2e File, 11 encapsulated postscript file

Equation of state for pure SU(3) gauge theory with renormalization group improved action

A lattice study of the equation of state for pure SU(3) gauge theory using a renormalization-group (RG) improved action is presented. The energy density and pressure are calculated on a $16^3\times 4$ and a $32^3\times 8$ lattice employing the integral method. Extrapolating the results to the continuum limit, we find the energy density and pressure to be in good agreement with those obtained with the standard plaquette action within the error of 3-4%.Comment: 17 pages, 14 figures, revte

Charmonium properties in hot quenched lattice QCD

We study the properties of charmonium states at finite temperature in quenched QCD on large and fine isotropic lattices. We perform a detailed analysis of charmonium correlation and spectral functions both below and above $T_c$. Our analysis suggests that both S wave states ($J/\psi$ and $\eta_c$) and P wave states ($\chi_{c0}$ and $\chi_{c1}$) disappear already at about $1.5 T_c$. The charm diffusion coefficient is estimated through the Kubo formula and found to be compatible with zero below $T_c$ and approximately $1/\pi T$ at $1.5 T_c\lesssim T\lesssim 3 T_c$.Comment: 32 pages, 19 figures, typo corrected, discussions on isotropic vs anisotropic lattices expanded, published versio

Dark radiation as a signature of dark energy

We propose a simple dark energy model with the following properties: the model predicts a late-time dark radiation component that is not ruled out by current observational data, but which produces a distinctive time-dependent equation of state w(z) for z < 3. The dark energy field can be coupled strongly enough to Standard Model particles to be detected in colliders, and the model requires only modest additional particle content and little or no fine-tuning other than a new energy scale of order milli-electron volts.Comment: 6 pages, 5 figures, revtex; v2: footnote 3 added, minor changes, published versio

Infinite temperature limit of meson spectral functions calculated on the lattice

We analyze the cut-off dependence of mesonic spectral functions calculated at finite temperature on Euclidean lattices with finite temporal extent. In the infinite temperature limit we present analytic results for lattice spectral functions calculated with standard Wilson fermions as well as a truncated perfect action. We explicitly determine the influence of `Wilson doublers' on the high momentum structure of the mesonic spectral functions and show that this cut-off effect is strongly suppressed when using an improved fermion action.Comment: 25 pages, 8 figure

Domain Wall Dynamics of Phase Interfaces

The statics and dynamics of a surface separating two phases of a relativistic quantum field theory at or near the critical temperature typically make use of a free energy as a functional of an order parameter. This free energy functional also affords an economical description of states away from equilibrium. The similarities and differences between using a scalar field as the order parameter versus the energy density are examined, and a peculiarity is noted. We also point out several conceptual errors in the literature dealing with the dynamical prefactor in the nucleation rate.Comment: 12 pages plus 5 figure

Heavy Quark Potentials in Quenched QCD at High Temperature

Heavy quark potentials are investigated at high temperatures. The temperature range covered by the analysis extends from $T$ values just below the deconfinement temperature up to about $4 T_c$ in the deconfined phase. We simulated the pure gauge sector of QCD on lattices with temporal extents of 4, 6 and 8 with spatial volumes of $32^3$. On the smallest lattice a tree level improved action was employed while in the other two cases the standard Wilson action was used. Below $T_c$ we find a temperature dependent logarithmic term contributing to the confinement potential and observe a string tension which decreases with rising temperature but retains a finite value at the deconfinement transition. Above $T_c$ the potential is Debye-screened, however simple perturbative predictions do not apply.Comment: 20 pages, 9 figure

Preservation of granulite in a partially eclogitized terrane: Metastable phenomena or local pressure variations?

Granulite is preserved over large areas of partially eclogitized and hydrated rocks on Holsnøy, Bergen Arcs, Norway. The interfaces between granulite and eclogite are sharp on a hand-specimen scale and contain microstructural and compositional evidence for the mechanism of eclogitization. The interface studied here is undeformed with a continuous foliation from granulite through an eclogite ‘finger’ that protrudes into the granulite. Diopside in the granulite evolves continuously to omphacite in eclogite by increasing jadeite composition at a well-defined sequence of microstructures that involve pyroxene-amphibole intergrowths and symplectites. Plagioclase in the granulite develops a high density of zoisite and kyanite inclusions that increase in abundance prior to plagioclase breakdown in eclogite. The transition between granulite and eclogite is interpreted as indicating a pressure gradient. The observation that granulite is preserved adjacent to eclogite although it shows sufficient evidence of hydration such that metastability may not be a factor, suggests that eclogitization involves the generation of increased pressure due to reaction and rock weakening. The pyroxene and feldspar microstructures in the transition zone between granulite and eclogite are very similar to the transition zones between granulite and amphibolite elsewhere in the Bergen Arcs. Localized variation in pressure could be an explanation for concurrent eclogitization and amphibolitization of granulite at the same crustal level during orogenesis