40,341 research outputs found
The topological susceptibility in `full' (UK)QCD
We report first calculations of the topological susceptibility measured using
the field theoretic method on SU(3) gauge configurations produced by the UKQCD
collaboration with two flavours of dynamical, improved, Wilson fermions. Using
three ensembles with matched lattice spacing but differing sea quark mass we
find that hybrid Monte Carlo simulation appears to explore the topological
sectors efficiently, and a topological susceptibility consistent with
increasing linearly with the quark mass.Comment: LaTeX. 4 PostScript figures. Contribution to LATTICE99(topology
Instantons and Monopoles in the Maximally Abelian Gauge
We study the Abelian projection of SU(2) instantons in the Maximally Abelian
gauge. We find that in this gauge an isolated instanton produces a closed
monopole loop within its core and the size of this loop increases with the core
size. We show that this result is robust against the introduction of small
quantum fluctuations. We investigate the effects of neighbouring
(anti)instantons upon each other and show how overlapping (anti)instantons can
generate larger monopole loops. We find, however, that in fields that are
typical of the fully quantised vacuum only some of the large monopole loops
that are important for confinement have a topological origin. We comment on
what this may imply for the role of instantons in confinement and chiral
symmetry breaking.Comment: 14 pages LaTeX plus 5 PostScript figures. Uses epsf.sty.
Self-unpacking, uuencoded tar-compressed fil
Monopole clusters in Abelian projected gauge theories
We show that the monopole currents which one obtains in the maximally Abelian
gauge of SU(2) fall into two quite distinct classes (when the volume is large
enough). In each field configuration there is precisely one cluster that
permeates the whole lattice volume. It has a current density and a magnetic
screening mass that scale and it produces the whole of the string tension. The
remaining clusters have a number density that follows an approximate power law
proportional to the inverse cube of l where l is the length of the monopole
world line in lattice units. These clusters are localised in space-time with
radii which vary as the square root of l. In terms of the radius r these
`lumps' have a scale-invariant distribution proportional to (dr/r . 1/{r^4}).
Moreover they appear not to contribute at all to the string tension. The fact
that they are scale-invariant at small distances would seem to rule out an
instanton origin.Comment: LaTeX, 31 pages, 11 PostScript figures. Typo in Table 2 correcte
The U.S. Gulf of Mexico Pink Shrimp, Farfantepenaeus duorarum, Fishery: 50 Years of Commercial Catch Statistics
U.S. Gulf of Mexico, pink shrimp, Farfantepenaeus duorarum, catch statistics have been collected by NOAA’s National Marine Fisheries Service, or its predecessor agency, for over 50 years. Recent events, including hurricanes and oil spills within the ecosystem of the fishery, have shown that documentation of these catch data is of primary importance. Fishing effort for this stock has fluctuated over the 50-year period analyzed, ranging from 3,376 to 31,900 days fished, with the most recent years on record, 2008 and 2009, exhibiting declines up to 90% relative to the high levels recorded in the mid 1990’s. Our quantification of F. duorarum landings and catch rates (CPUE) indicates catch have been below the long-term average of about 12 million lb for all of the last 10 years on record. In contrast to catch and effort, catch rates have increased in recent years, with record CPUE levels measured in 2008 and 2009, of 1,340 and 1,144 lb per day fished, respectively. Our regression results revealed catch was dependent upon fishing effort (F=98.48df=1, 48, p<0.001, r2=0.67), (Catch=1,623,378 + (520) × (effort)). High CPUE’s measured indicate stocks were not in decline prior to 2009, despite the decline in catch. The decrease in catch is attributed in large part to low effort levels caused by economical and not biological or habitat related conditions. Future stock assessments using these baseline data will provide further insights and management advice concerning the Gulf of Mexi
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
Radiative corrections to the lattice gluon action for highly improved staggered quarks (HISQ) and the effect of such corrections on the static potential
We perform a perturbative calculation of the influence of dynamical HISQ
fermions on the perturbative improvement of the gluonic action in the same way
as we have previously done for asqtad fermions. We find the fermionic
contributions to the radiative corrections in the Luescher-Weisz gauge action
to be somewhat larger for HISQ fermions than for asqtad. Using one-loop
perturbation theory as a test, we estimate that omission of the fermion-induced
radiative corrections in dynamical asqtad simulations will give a measurable
effect. The one-loop result gives a systematic shift of about -0.6% in (r_1/a)
on the coarsest asqtad improved staggered ensembles. This is the correct sign
and magnitude to explain the scaling violations seen in Phi_B on dynamical
lattice ensembles.Comment: 10 pages, 5 figures. Minor corrections suggested by refere
Monopole Spectra in non-Abelian Gauge Theories
We study the continuum limit of the length spectrum of magnetic monopole
structures found after various Abelian projections of pure gauge SU(2),
including the maximally Abelian gauge. We comment on Gribov copies, and
measurements of the string tension.Comment: Talk presented at LATTICE96(topology) LaTeX, with 4 LaTeX figure
Z2 monopoles in D=2+1 SU(2) lattice gauge theory
We calculate the Euclidean action of a pair of Z2 monopoles (instantons), as
a function of their spatial separation, in D=2+1 SU(2) lattice gauge theory. We
do so both above and below the deconfining transition at T=Tc. At high T, and
at large separation, we find that the monopole `interaction' grows linearly
with distance: the flux between the monopoles forms a flux tube (exactly like a
finite portion of a Z2 domain wall) so that the monopoles are linearly
confined. At short distances the interaction is well described by a Coulomb
interaction with, at most, a very small screening mass, possibly equal to the
Debye electric screening mass. At low T the interaction can be described by a
simple screened Coulomb (i.e. Yukawa) interaction with a screening mass that
can be interpreted as the mass of a `constituent gluon'. None of this is
unexpected, but it helps to resolve some apparent controversies in the recent
literature.Comment: 14 pages, 2 figure
Vortices and confinement in hot and cold D=2+1 gauge theories
We calculate the variation with temperature of the vortex free energy in
D=2+1 SU(2) lattice gauge theories. We do so both above and below the
deconfining transition at T=Tc. We find that this quantity is zero at all T for
large enough volumes. For T<Tc this observation is consistent with the fact
that the phase is linearly confining; while for T>Tc it is consistent with the
conventional expectation of `spatial' linear confinement. In small spatial
volumes this quantity is shown to be non-zero. The way it decreases to zero
with increasing volume is shown to be controlled by the (spatial) string
tension and it has the functional form one would expect if the vortices being
studied were responsible for the confinement at low T, and for the `spatial'
confinement at large T. We also discuss in detail some of the direct numerical
evidence for a non-zero spatial string tension at high T, and we show that the
observed linearity of the (spatial) potential extends over distances that are
large compared to typical high-T length scales.Comment: 27 pages, 6 figure
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