2,418 research outputs found
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
Vortex structures in pure SU(3) lattice gauge theory
The structures of confining vortices which underlie pure SU(3) Yang-Mills
theory are studied by means of lattice gauge theory. Vortices and Z_3 monopoles
are defined as dynamical degrees of freedom of the Z_3 gauge theory which
emerges by center gauge fixing and by subsequent center projection. It is
observed for the first time for the case of SU(3) that these degrees of freedom
are sensible in the continuum limit: the planar vortex density and the monopole
density properly scales with the lattice spacing. By contrast to earlier
findings concerning the gauge group SU(2), the effective vortex theory only
reproduces 62% of the full string tension. On the other hand, however, the
removal of the vortices from the lattice configurations yields ensembles with
vanishing string tension. SU(3) vortex matter which originates from Laplacian
center gauge fixing is also discussed. Although these vortices recover the full
string tension, they lack a direct interpretation as physical degrees of
freedom in the continuum limit.Comment: 25 pages, 13 ps figures, improved presentation, results unchange
Gribov Copies in the Maximally Abelian Gauge and Confinement
We fix lattice gauge fields to the Maximally Abelian gauge in both
three and four dimensions. We extract the corresponding fields and
monopole current densities and calculate separately the confining string
tensions arising from these fields and monopole `condensates'. We
generate multiple Gribov copies and study how the fields and monopole
distributions vary between these different copies. As expected, we find
substantial variations in the number of monopoles, their locations and in the
values of the field strengths. The string tensions extracted from
`extreme' Gribov copies also differ but this difference appears to be no more
than about 20\%. We also directly compare the fields of different Gribov
copies. We find that on the distance scales relevant to confinement the
and monopole fluxes that disorder Wilson loops are highly correlated between
these different Gribov copies. All this suggests that while there is indeed a
Gribov copy problem the resulting ambiguity is, in this gauge and for the study
of confinement, of limited importance.Comment: 31 pages LaTeX plus 5 PostScript figures. Uses epsf.sty.
Self-unpacking, uuencoded tar-compressed fil
Three-Quark Potential in SU(3) Lattice QCD
The static three-quark (3Q) potential is measured in the SU(3) lattice QCD
with and at the quenched level. From the 3Q Wilson
loop, the 3Q ground-state potential is extracted using the
smearing technique for the ground-state enhancement. With accuracy better than
a few %, is well described by a sum of a constant, the two-body
Coulomb term and the three-body linear confinement term , where denotes the minimal length of the color flux tube
linking the three quarks. By comparing with the Q- potential, we
find a universal feature of the string tension, , as well as the one-gluon-exchange result for the
Coulomb coefficient, .Comment: 7 pages, 3 figur
Ab Initio Calculation of Relativistic Corrections to the Static Interquark potential I: SU(2) Gauge Theory
We test the capability of state-of-the-art lattice techniques for a precise
determination of relativistic corrections to the static interquark potential,
by use of SU(2) gauge theory. Emphasis is put on the short range structure of
the spin dependent potentials, with lattice resolution a ranging from a approx
0.04 fm (at beta=2.74) down to a approx 0.02 fm (at beta=2.96) on volumes of
32^4 and 48^4 lattice sites. We find a new short range Coulomb-like
contribution to the spin-orbit potential V_1'.Comment: 37 pages REVTeX with 20 encapsuled ps figure
Bianchi Type V Viscous Fluid Cosmological Models in Presence of Decaying Vacuum Energy
Bianchi type V viscous fluid cosmological model for barotropic fluid
distribution with varying cosmological term is investigated. We have
examined a cosmological scenario proposing a variation law for Hubble parameter
in the background of homogeneous, anisotropic Bianchi type V space-time.
The model isotropizes asymptotically and the presence of shear viscosity
accelerates the isotropization. The model describes a unified expansion history
of the universe indicating initial decelerating expansion and late time
accelerating phase. Cosmological consequences of the model are also discussed.Comment: 10 pages, 3 figure
Location, correlation, radiation: where is the , what is its structure and what is its coupling to photons?
Scalar mesons are a key expression of the infrared regime of QCD. The
lightest of these is the . Now that its pole in the complex energy
plane has been precisely located, we can ask whether this state is transiently
or or a multi-meson molecule or largely glue? The
two photon decay of the can, in principle, discriminate between these
possibilities. We review here how the ,
cross-sections can be accurately computed. The result not only agrees with
experiment, but definitively fixes the radiative coupling of the . This
equates to a two photon width of keV, which accords with the
simple non-relativistic quark model expectation for a
scalar. Nevertheless, robust predictions from relativistic strong coupling QCD
are required for each of the possible compositions before we can be sure which
one really delivers the determined coupling.Comment: 18 pages, 11 figures. To be published in Modern Physics Letters A A
number of references updated and three sentences changed in the text to
reflect thes
Topological Structure of the SU(3) Vacuum
We investigate the topological structure of the vacuum in SU(3) lattice gauge
theory. We use under-relaxed cooling to remove the high-frequency fluctuations
and a variety of "filters" to identify the topological charges in the resulting
smoothened field configurations. We find a densely packed vacuum with an
average instanton size, in the continuum limit, of about 0.5 fm. The density at
large sizes decreases as a large inverse power of the size. At small sizes we
see some sign of a trend towards the asymptotic perturbative behaviour. We find
that an interesting polarisation phenomenon occurs: the large topological
charges tend to have, on the average, the same sign and are over-screened by
the smaller charges which tend to have, again on the average, the opposite sign
to the larger instantons. We also calculate the topological susceptibility for
which we obtain a continuum value of about 187 MeV. We perform the calculations
for various volumes, lattice spacings and numbers of cooling sweeps, so as to
obtain some control over the associated systematic errors. The coupling range
is from beta=6.0 to beta=6.4 and the lattice volumes range from 16x16x16x48 to
32x32x32x64.Comment: LaTeX. Self-unpacking, uuencoded tar-compressed fil
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