Quark-Antiquark Forces From SU(2) and SU(3) Gauge Theories on Large Lattices

We present results on the spin-independent quark-antiquark potential in SU(3) gauge theory from a simulation on a 48^3*64 lattice at Beta = 6.8, corresponding to a volume of (1.7 fm)^3. Moreover, a comprehensive analysis of spin- and velocity-dependent potentials is carried out for SU(2) gauge theory, with emphasis on the short range structure, on lattices with resolutions ranging from .02 fm to .04 fm.Comment: 10 pages, uucompressed latex with 5 ps figures, epsf style require

Where do perturbative and non-perturbative QCD meet?

We computed the static potential and Wilson loops to $O(\alpha^2)$ in perturbation theory for different lattice quark and gluon actions. In general, we find short distance lattice data to be well described by ``boosted perturbation theory''. For Wilson-type fermions at present-day quark masses and lattice spacings agreement within 10% between measured ``$\beta$-shifts'' and those predicted by perturbation theory is found. We comment on prospects for a determination of the real world QCD running coupling.Comment: 3 pages, 4 figures, Talk at Lattice 2001 in renormalisation and improvement sessio

The Running Coupling from SU(3) Gauge Theory

We present high precision results on the static quark-antiquark-potential on 32^4 and smaller lattices, using the standard Wilson action at BETA = 6.0, 6.2, 6.4, and 6.8 on the Connection Machine CM-2. Within our statistical errors (1%) we did not observe any finite size effects affecting the potential values, on varying the spatial lattice extent from 0.9 fm up to 3.3 fm. We find violations of asymptotic scaling in the bare coupling up to BETA = 6.8. We demonstrate that scaling violations on the string tension can be considerably reduced by introducing effective coupling schemes, which allow for a safer extrapolation of LAMBDA_Lattice to its continuum value. We are also able to see and to quantify the running of the coupling from the interquark force. From this we extract the ratio \sqrt{SIGMA}/LAMBDA_L. Both methods yield consistent values for the LAMBDA-parameter: LAMBDA_MSbar = 0.558(-0.007+0.017)\sqrt{SIGMA} = 246(-3+7) MeV.Comment: (Talk G. Bali at Lattice 92, Amsterdam), 4 Pages, 4 Postscript figures, LaTeX with espcrc2, and epsf style file

SU(2) Colour Fields Around Static Sources

First results of an ongoing high statistics study of the colour flux distribution around static quark sources in SU(2) gauge theory are presented. The flux tube profiles and widths have been investigated for several quark separations at beta=2.5 and beta=2.74. The results are tested against Michael's sum rules.Comment: 3 pages (LaTeX) with 4 epsf incl. PS figs., To be publ. in Proc. of Lattice '9

String breaking

We numerically investigate the transition of the static quark-antiquark string into a static-light meson-antimeson system. Improving noise reduction techniques, we are able to resolve the signature of string breaking dynamics for Nf=2 lattice QCD at zero temperature. We discuss the lattice techniques used and present results on energy levels and mixing angle of the static two-state system. We visualize the action density distribution in the region of string breaking as a function of the static colour source-antisource separation. The results can be related to properties of quarkonium systems.Comment: 8 pages, Talk given at the Workshop on Computational Hadron Physics, Nicosia, Cyprus, 14--17 September 200

A Ginzburg-Landau Analysis of the Colour Electric Flux Tube

In a simulation of SU(2) gauge theory we investigate, after maximal Abelian projection, the dual Maxwell equations for colour field and monopole current distributions around a static quark-antiquark pair Q_ Q in vacuo. Within the dual superconductor picture we carry out a Ginzburg-Landau type analysis of the flux tube profile. As a result we can determine the coherence length of the GL wave function related to the monopole condensate, xi = .25(3) fm, to be compared to the penetration length, lambda = >.15(2) fm (scaled with the string tension).Comment: 3 pages, 5 figures, corrected typos, LATTICE98(confine

Alpha_s from the Lattice Potential

We present an extensive study on the direct determination of the running coupling alpha_s from the static quark antiquark force at short distances, in quenched QCD. We find from our high statistics potential analysis that alpha_qq exhibits two-loop asymptotic behaviour for momenta as low as .5 GeV. As a result, we determine the zero flavour Lambda-parameter to be Lambda^0_MSBAR = 0.630(38)\sqrt{\sigma} = 293(18)^{+25}_{-63} MeV. A rough estimate of full QCD effects leads to the five flavour value alpha_MSBAR(m_Z) = .102^{+6}_{-11}. A comparison with other lattice results is made.Comment: 6 pages (LaTeX) with 7 postscript figures (epsf required), Invited talk by K. Schilling held at Lattice '93 conference, Dallas, T

Color Flux Profiles in SU(2) Lattice Gauge Theory

Results of a high statistics study of chromo field distributions around static sources in pure SU(2) gauge theory on lattices of volumes $16^4$, $32^4$, and $48^3\times 64$ at $\beta=2.5$, $2.635$, and $2.74$ are presented. We establish string formation up to physical distances as large as 2 fm.Comment: Contribution to Lattice '94, 3 pages uu-compressed LaTeX + 3 psfig

The Spatial String Tension in the Deconfined Phase of the (3+1)-Dimensional SU(2) Gauge Theory

We present results of a detailed investigation of the temperature dependence of the spatial string tension in SU(2) gauge theory. We show, for the first time, that the spatial string tension is scaling on the lattice and thus is non-vanishing in the continuum limit. It is temperature independent below Tc and rises rapidly above. For temperatures larger than 2Tc we find a scaling behaviour consistent with sigma_s(T) = 0.136(11) g^4(T) T^2, where g(T) is the 2-loop running coupling constant with a scale parameter determined as Lambda_T = 0.076(13) Tc.Comment: 8 pages (Latex, shell archive, 3 PostScript figures), HLRZ-93-43, BI-TP 93/30, FSU-SCRI-93-76, WUB 93-2

Spin dependent potentials from SU(2) gauge theory

We present results on spin dependent potentials from lattice simulations of SU(2) gauge theory. The Coulomb like short range part of the central potential is identified as a mixed vector-scalar exchange while the linear long range part is pure scalar.Comment: Talk held at LAT 94 conference, 3 pages, latex, uses epscrc2.st