Properties of Color-Coulomb String Tension

We study the properties of the color-Coulomb string tension obtained from the instantaneous part of gluon propagators in Coulomb gauge using quenched SU(3) lattice simulation. In the confinement phase, the dependence of the color-Coulomb string tension on the QCD coupling constant is smaller than that of the Wilson loop string tension. On the other hand, in the deconfinement phase, the color-Coulomb string tension does not vanish even for $T/T_c = 1 \sim 5$, the temperature dependence of which is comparable with the magnetic scaling, dominating the high temperature QCD. Thus, the color-Coulomb string tension is not an order parameter of QGP phase transition.Comment: 17 pages, 5 figures; one new figure added, typos corrected, version to appear in PR

Spatial string tension revisited

The spatial string tension, a classic non-perturbative probe for the convergence of the weak-coupling expansion at high temperatures, can be determined in full QCD as well as in a dimensionally reduced effective theory. Comparing both approaches, we find surprisingly good agreement almost down to the critical temperature of the deconfinement phase transition.Comment: 6 pages, 2 figures, talk given at Lattice 2005 (nonzero temperature and density

The QCD string tension curve, the ferromagnetic magnetization, and the quark-antiquark confining potential at finite Temperature

We study the string tension as a function of temperature, fitting the SU(3) lattice QCD finite temperature free energy potentials computed by the Bielefeld group. We compare the string tension points with order parameter curves of ferromagnets, superconductors or string models, all related to confinement. We also compare the SU(3) string tension with the one of SU(2) Lattice QCD. With the curve providing the best fit to the finite temperature string tensions, the spontaneous magnetization curve, we then show how to include finite temperature, in the state of the art confining and chiral invariant quark models.Comment: 9 pages, 12 figure

Some remarks on Abelian dominance

We use a renormalisation group based smoothing to address two questions related to Abelian dominance. Smoothing enables us to extract the Abelian heavy-quark potential from time-like Wilson loops on Polyakov gauge projected configurations. We obtained a very small string tension which is inconsistent with the string tension extracted from Polyakov loop correlators. This shows that the Polyakov gauge projected Abelian configurations do not have a consistent physical meaning. We also apply the smoothing on SU(2) configurations to test how sensitive Abelian dominance in the maximal Abelian gauge is to the short distance fluctuations. We find that on smoothed SU(2) configurations the Abelian string tension was about 30% smaller than the SU(2) string tension which was unaffected by smoothing. This suggests that the approximate Abelian dominance found with the Wilson action is probably an accident and it has no fundamental physical relevance.Comment: 3 pages, LaTeX, 1 figure, uses espcrc2.sty, Talk given at LATTICE9

Magnetic monopole clusters, and monopole dominance after smoothing in the maximally Abelian gauge of SU(2)

In the maximally Abelian gauge of SU(2), the clusters of monopole current are found to divide into two distinct classes. The largest cluster permeates the lattice, has a density that scales and produces the string tension. The remaining clusters possess an approximate 1/l^3 number density distribution (l is the cluster length), their radii vary as \sqrt l and their total current density does not scale. Their contribution to the string tension is compatible with being exactly zero. Their number density can be thought of as arising from an underlying scale invariant distribution. This suggests that they are not related to instantons. We also observe that when we locally smoothen the SU(2) fields by cooling, the string tension due to monopoles becomes much smaller than the SU(2) string tension. This dramatic loss of Abelian/monopole dominance occurs even after just one cooling step.Comment: Talk presented at LATTICE97(topology). LaTeX, with 4 PS figure

P-vortices and Drama of Gribov Copies

We present results of the careful study of the Gribov copies problem in SU(2) lattice gauge theory for the direct maximal center projection widely used in confinement studies. Applying simulated annealing algorithm we demonstrate that this problem is more severe than it was thought before. The projected (gauge noninvariant) string tension is not in the agreement with the physical string tension. We do not find any indications that P-vortices reproduce the full SU(2) string tension neither in the infinite volume limit nor in the continuum limit.Comment: 16 pages, 7 figures, Latex2e, typos correcte

Spatial string tension in Nf=2N_f=2 lattice QCD at finite temperature

The spatial string tension across a crossover from the low temperature phase to the high temperature phase is computed in QCD with two flavors of non-perturbatively improved Wilson fermions at small lattice spacing a \sim 0.12fm. We find that in the low temperature phase spatial string tension agrees well with zero temperature string tension. Furthermore, it does not show increasing for temperatures up to T = 1.36 T_{pc}, the highest temperature considered. Our results agree with some theoretical predictions.Comment: 8 pages, 2 figures, numerical results and both figures slightly changed, comparison with theoretical predictions added, values of the ratio T/T_{pc} slightly change