1,197 research outputs found
High energy parton-parton amplitudes from lattice QCD and the stochastic vacuum model
Making use of the gluon gauge-invariant two-point correlation function,
recently determined by numerical simulation on the lattice in the quenched
approximation and the stochastic vacuum model, we calculate the elementary
(parton-parton) amplitudes in both impact-parameter and momentum transfer
spaces. The results are compared with those obtained from the Kr\"{a}mer and
Dosch ansatz for the correlators. Our main conclusion is that the divergences
in the correlations functions suggested by the lattice calculations do not
affect substantially the elementary amplitudes. Phenomenological and
semiempirical information presently available on elementary amplitudes is also
referred to and is critically discussed in connection with some theoretical
issues.Comment: Text with 11 pages in LaTeX (twocolumn form), 10 figures in
PostScript (psfig.tex used). Replaced with changes, Fig.1 modified, two
references added, some points clarified, various typos corrected. Version to
appear in Phys. Rev.
Low temperature relation for the trace of the energy-momentum tensor in QCD with light quarks
It is shown that the temperature derivatives of the anomalous and normal
(quark massive term) contributions to the trace of the energy-momentum tensor
in QCD are equal to each other in the low temperature region. The physical
consequences of this relation are discussed.Comment: RevTeX, 4 pages, no figure
A gauge invariant study of the monopole condensation in non Abelian lattice gauge theories
We investigate the Abelian monopole condensation in finite temperature SU(2)
and SU(3) pure lattice gauge theories. To this end we introduce a gauge
invariant disorder parameter built up in terms of the lattice Schr\"odinger
functional. Our numerical results show that the disorder parameter is different
from zero and Abelian monopole condense in the confined phase. On the other
hand our numerical data suggest that the disorder parameter tends to zero, in
the thermodynamic limit, when the gauge coupling constant approaches the
critical deconfinement value. In the case of SU(3) we also compare the
different kinds of Abelian monopoles which can be defined according to the
choice of the Abelian subgroups.Comment: 18 pages, 7 figures, LaTe
The 2-dimensional non-linear sigma-model on a random latice
The O(n) non-linear -model is simulated on 2-dimensional regular and
random lattices. We use two different levels of randomness in the construction
of the random lattices and give a detailed explanation of the geometry of such
lattices. In the simulations, we calculate the mass gap for and 8,
analysing the asymptotic scaling of the data and computing the ratio of Lambda
parameters . These ratios are in
agreement with previous semi-analytical calculations. We also numerically
calculate the topological susceptibility by using the cooling method.Comment: REVTeX file, 23 pages. 13 postscript figures in a separate compressed
tar fil
Low temperature relations in QCD
In this talk I discuss the low temperature relations for the trace of the
energy-momentum tensor in QCD with two and three quarks. It is shown that the
temperature derivatives of the anomalous and normal (quark massive term)
contributions to the trace of the energy-momentum tensor in QCD are equal to
each other in the low temperature region. Leading corrections connected with
-interactions and thermal excitations of and mesons are
calculated.Comment: 10 pages, LaTeX2e. Talk given at 12th International Seminar on
High-Energy Physics (QUARKS 2002), Novgorod, Russia, 1-7 Jun 200
Test of the QCD vacuum with the sources in higher representations
Recent accurate measurement by G.Bali of static potentials between sources in
various SU(3) representations provides a crucial test of the QCD vacuum and of
different theoretical approaches to the confinement. In particular, the Casimir
scaling of static potentials found for all measured distances implies a strong
suppression of higher cumulants and a high accuracy of the Gaussian stochastic
vacuum. Most popular models are in conflict with these measurements.Comment: LaTeX, 7 page
Decorrelating Topology with HMC
The investigation of the decorrelation efficiency of the HMC algorithm with
respect to vacuum topology is a prerequisite for trustworthy full QCD
simulations, in particular for the computation of topology sensitive
quantities. We demonstrate that for mpi/mrho ratios <= 0.69 sufficient
tunneling between the topological sectors can be achieved, for two flavours of
dynamical Wilson fermions close to the scaling region beta=5.6. Our results are
based on time series of length 5000 trajectories.Comment: change of comments: LATTICE98(confine
On projection (in)dependence of monopole condensate in lattice SU(2) gauge theory
We study the temperature dependence of the monopole condensate in different
Abelian projections of the SU(2) lattice gauge theory. Using the
Frohlich-Marchetti monopole creation operator we show numerically that the
monopole condensate depends on the choice of the Abelian projection. Contrary
to the claims in the current literature we observe that in the Abelian Polyakov
gauge and in the field strength gauge the monopole condensate does not vanish
at the critical temperature and thus is not an order parameter.Comment: 9 pages, 7 figure
Lower-dimension vacuum defects in lattice Yang-Mills theory
We overview lattice data on d=1,2,3 vacuum defects in four-dimensional
gluodynamics. In all the cases defects have total volume which scales in
physical units (with zero fractal dimension). In case of d=1,2 the defects are
distinguished by ultraviolet divergent non-Abelian action as well. This
sensitivity to the ultraviolet scale allows to derive from the continuum theory
strong constraints on the properties of the defects. The constraints turn to be
satisfied by the lattice data. In the SU(2) case we introduce a classification
scheme of the defects which allows to (at least) visualize the defect
properties in a simple and unified way. Not-yet-checked relation of the defects
to the spontaneous chiral symmetry breaking is suggested by the scheme.Comment: 19 pages Dedicated to Yuri A. Simonov on his 70th birthda
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