166 research outputs found

### 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

### Casimir scaling of SU(3) static potentials

Potentials between static colour sources in eight different representations
are computed in four dimensional SU(3) gauge theory. The simulations have been
performed with the Wilson action on anisotropic lattices where the renormalised
anisotropies have been determined non-perturbatively. After an extrapolation to
the continuum limit we are able to exclude any violations of the Casimir
scaling hypothesis that exceed 5% for source separations of up to 1 fm.Comment: 12 pages, 10 figures, RevTeX, v2: 1 reference added, more explanation
about advantages of anisotrop

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