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

SU(3) Latent Heat and Surface Tension from Tree Level and Tadpole Improved Actions

We analyze the latent heat and surface tension at the SU(3) deconfinement phase transition with tree level and tadpole improved Symanzik actions on lattices with temporal extent $N_\tau = 3$ and 4 and spatial extent $N_\sigma/ N_\tau = 4$, 6 and 8. In comparison to the standard Wilson action we do find a drastic reduction of cut-off effects already with tree level improved actions. On lattices with temporal extent $N_\tau=4$ results for the surface tension and latent heat obtained with a tree level improved action agree well with those obtained with a tadpole improved action. A comparison with $N_\tau=3$ calculations, however, shows that results obtained with tadpole action remain unaffected by cut-off effects even on this coarse lattice, while the tree level action becomes sensitive to the cut-off. For the surface tension and latent heat we find $\sigma_I/ T_c^3 = 0.0155~(16)$ and $\Delta\epsilon/T_c^4 = 1.40~(9)$, respectively.Comment: 11 pages, LaTeX2e File, 3 Postscript figure

Improved Actions for QCD Thermodynamics on the Lattice

Finite cut-off effects strongly influence the thermodynamics of lattice regularized QCD at high temperature in the standard Wilson formulation. We analyze the reduction of finite cut-off effects in formulations of the thermodynamics of $SU(N)$ gauge theories with three different $O(a^2)$ and $O(a^4)$ improved actions. We calculate the energy density and pressure on finite lattices in leading order weak coupling perturbation theory ($T\rightarrow \infty$) and perform Monte Carlo simulations with improved $SU(3)$ actions at non-zero $g^2$. Already on lattices with temporal extent $N_\tau=4$ we find a strong reduction of finite cut-off effects in the high temperature limit, which persists also down to temperatures a few times the deconfinement transition temperature.Comment: 20 pages, 3 Postscript figure

The three flavour chiral phase transition with an improved quark and gluon action in lattice QCD

The finite-temperature chiral phase transition is investigated for three flavours of staggered quarks on a lattice of temporal extent N_t=4. In the simulation we use an improved fermion action which reduces rotational symmetry breaking of the quark propagator (p4-action), include fat-links to improve the flavour symmetry and use the tree level improved (1,2) gluon action. We study the nature of the phase transition for quark masses of ma=0.025, ma=0.05 and ma=0.1 on lattices with spatial sizes of 8^3 and 16^3.Comment: LATTICE98(hightemp), 3 pages, 7 figures, LaTeX2e-File, espcrc2.st

The string tension in SU(N) gauge theory from a careful analysis of smearing parameters

We report a method to select optimal smearing parameters before production runs and discuss the advantages of this selection for the determination of the string tension.Comment: Contribution to Lat97 poster session, title was 'How to measure the string tension', 3 pages, 5 colour eps figure

Finite Temperature Transitions in Lattice QCD with Wilson Quarks --- Chiral Transitions and the Influence of the Strange Quark ---

The nature of finite temperature transitions in lattice QCD with Wilson quarks is studied near the chiral limit for the cases of 2, 3, and 6 flavors of degenerate quarks ($N_F=2$, 3, and 6) and also for the case of massless up and down quarks and a light strange quark ($N_F=2+1$). Our simulations mainly performed on lattices with the temporal direction extension $N_t=4$ indicate that the finite temperature transition in the chiral limit (chiral transition) is continuous for $N_F=2$, while it is of first order for $N_F=3$ and 6. We find that the transition is of first order for the case of massless up and down quarks and the physical strange quark where we obtain a value of $m_\phi/m_\rho$ consistent with the physical value. We also discuss the phase structure at zero temperature as well as that at finite temperatures.Comment: uuencoded compressed tar file, 70 pages, 32 figure

Four-dimensional Simulation of the Hot Electroweak Phase Transition with the SU(2) Gauge-Higgs Model

We study the finite-temperature phase transition of the four-dimensional SU(2) gauge-Higgs model for intermediate values of the Higgs boson mass in the range 50 \lsim m_H \lsim 100GeV on a lattice with the temporal lattice size $N_t=2$. The order of the transition is systematically examined using finite size scaling methods. Behavior of the interface tension and the latent heat for an increasing Higgs boson mass is also investigated.Comment: Talk presented at LATTICE96(electroweak), 3 pages of LaTeX, 4 PostScript figure

Interface Tension in Quenched QCD

We calculate the tension $\sigma$ of the interface between the confined and deconfined phases by the histogram method in SU(3) lattice gauge theory for temporal extents of 4 and 6 using the recent high-statistics data by QCDPAX collaboration. The results are $\sigma/T_c^3 = 0.0292(22)$ and 0.0218(33) for $N_t=4$ and 6, respectively. The ratio $\sigma/T_c^3$ shows a scaling violation similar to that already observed for the latent heat \latent. However, we find that the physically interesting dimensionless combinations (\sigma^{3}/\latent^2 T)^{1/2} and \sigma T/ \latent scale within the statistical errors.Comment: 13 pages with 2 PostScript figures, LaTeX, CERN-TH.6798/93, AZPH-TH/93-04, UTHEP-25

Spatial structure of quark Cooper pairs in a color superconductor

Spatial structure of Cooper pairs with quantum numbers color 3^*, I=J=L=S=0 in ud 2 flavor quark matter is studied by solving the gap equation and calculating the coherence length in full momentum range without the weak coupling approximation. Although the gap at the Fermi surface and the coherence length depend on density weakly, the shape of the r-space pair wave function varies strongly with density. This result indicates that quark Cooper pairs become more bosonic at higher densities.Comment: 10 pages, 3 figures. The frequency dependence of the gap and the limitation on the type I/type II discussion are mentioned briefly. To appear in Phys. Rev.

Surface Tension at Finite Tempearture in the MIT Bag Model

At $T = 0$ the surface tension $\sigma ^{1/3}$ in the MIT bag model for a single hadron is known to be negligible as compared to the bag pressure $B^{1/4}$. We show that at finite temperature it has a substantial value of 50 - 70 MeV which also differ from hadron to hadron. We also find that the dynamics of the Quark-Gluon Plasma is such that the creation of hybrids $(s\bar{s}g)$ with massive quarks will predominate over the creation of $(s\bar{s})$ mesons.Comment: Substantial changes in the revised version and a new author included, 13 pages in Latex and one figur