491 research outputs found
Analytic calculation of color-Coulomb potential and color confinement
We develop a calculational scheme in Coulomb and temporal gauge that respects
gauge invariance and is most easily applied to the infrared asymptotic region
of QCD. It resembles the Dyson-Schwinger equations of Euclidean quantum field
theory in Landau gauge, but is 3-dimensional. A simple calculation yields a
color-Coulomb potential that behaves at large approximately like for spatial dimension . This
is a linearly rising potential plus a rather weak dependence on .Comment: 12 page
Relations between the Gribov-horizon and center-vortex confinement scenarios
We review numerical evidence on connections between the center-vortex and
Gribov-horizon confinement scenarios.Comment: Plenary talk presented by S. Olejnik at "Quark Confinement and the
Hadron Spectrum VI", Villasimius, Sardinia, Italy, Sep. 21-25, 2004; 10
pages, 11 EPS figures, uses AIP Proceedings style file
Density-operator theory of orbital magnetic susceptibility in periodic insulators
The theoretical treatment of homogeneous static magnetic fields in periodic
systems is challenging, as the corresponding vector potential breaks the
translational invariance of the Hamiltonian. Based on density operators and
perturbation theory, we propose, for insulators, a periodic framework for the
treatment of magnetic fields up to arbitrary order of perturbation, similar to
widely used schemes for electric fields. The second-order term delivers a new,
remarkably simple, formulation of the macroscopic orbital magnetic
susceptibility for periodic insulators. We validate the latter expression using
a tight-binding model, analytically from the present theory and numerically
from the large-size limit of a finite cluster, with excellent numerical
agreement.Comment: 5 pages including 2 figures; accepted for publication in Phys. Rev.
Numerical Study of Gluon Propagator and Confinement Scenario in Minimal Coulomb Gauge
We present numerical results in SU(2) lattice gauge theory for the
space-space and time-time components of the gluon propagator at equal time in
the minimal Coulomb gauge. It is found that the equal-time would-be physical
3-dimensionally transverse gluon propagator vanishes at
when extrapolated to infinite lattice volume, whereas the
instantaneous color-Coulomb potential is strongly enhanced at
. This has a natural interpretation in a confinement scenario in
which the would-be physical gluons leave the physical spectrum while the
long-range Coulomb force confines color. Gribov's formula provides an excellent fit to our data
for the 3-dimensionally transverse equal-time gluon propagator
for relevant values of .Comment: 23 pages, 12 figures, TeX file. Minor modifications, incorporating
referee's suggestion
Lifting the Gribov ambiguity in Yang-Mills theories
We propose a new one-parameter family of Landau gauges for Yang-Mills
theories which can be formulated by means of functional integral methods and
are thus well suited for analytic calculations, but which are free of Gribov
ambiguities and avoid the Neuberger zero problem of the standard Faddeev-Popov
construction. The resulting gauge-fixed theory is perturbatively renormalizable
in four dimensions and, for what concerns the calculation of ghost and gauge
field correlators, it reduces to a massive extension of the Faddeev-Popov
action. We study the renormalization group flow of this theory at one-loop and
show that it has no Landau pole in the infrared for some - including physically
relevant - range of values of the renormalized parameters.Comment: 8 pages, 1 figure; published version (PLB), minor corrections,
references adde
Hospital competition, resource allocation and quality of care
BACKGROUND: A variety of approaches have been used to contain escalating hospital costs. One approach is intensifying price competition. The increase in price based competition, which changes the incentives hospitals face, coupled with the fact that consumers can more easily evaluate the quality of hotel services compared with the quality of clinical care, may lead hospitals to allocate more resources into hotel rather than clinical services. METHODS: To test this hypothesis we studied hospitals in California in 1982 and 1989, comparing resource allocations prior to and following selective contracting, a period during which the focus of competition changed from quality to price. We estimated the relationship between clinical outcomes, measured as risk-adjusted-mortality rates, and resources. RESULTS: In 1989, higher competition was associated with lower clinical expenditures levels compared with 1982. The trend was stronger for non-profit hospitals. Lower clinical resource use was associated with worse risk adjusted mortality outcomes. CONCLUSIONS: This study raises concerns that cost reductions may be associated with increased mortality
Landau gauge within the Gribov horizon
We consider a model which effectively restricts the functional integral of
Yang--Mills theories to the fundamental modular region. Using algebraic
arguments, we prove that this theory has the same divergences as ordinary Yang
Mills theory in the Landau gauge and that it is unitary. The restriction of the
functional integral is interpreted as a kind of spontaneous breakdown of the
symmetry.Comment: 17 pages, NYU-TH-93/10/0
High-Temperature Limit of Landau-Gauge Yang-Mills Theory
The infrared properties of the high-temperature limit of Landau-gauge
Yang-Mills theory are investigated. In a first step the high-temperature limit
of the Dyson-Schwinger equations is taken. The resulting equations are
identical to the Dyson-Schwinger equations of the dimensionally reduced theory,
a three-dimensional Yang-Mills theory coupled to an effective adjoint Higgs
field. These equations are solved analytically in the infrared and ultraviolet,
and numerically for all Euclidean momenta. We find infrared enhancement for the
Faddeev-Popov ghosts, infrared suppression for transverse gluons and a mass for
the Higgs. These results imply long-range interactions and over-screening in
the chromomagnetic sector of high temperature Yang-Mills theory while in the
chromoelectric sector only screening is observed.Comment: 21 pages, 23 figures, 3 tables, submitted to EPJ
Coulomb Energy, Vortices, and Confinement
We estimate the Coulomb energy of static quarks from a Monte Carlo
calculation of the correlator of timelike link variables in Coulomb gauge. We
find, in agreement with Cucchieri and Zwanziger, that this energy grows
linearly with distance at large quark separations. The corresponding string
tension, however, is several times greater than the accepted asymptotic string
tension, indicating that a state containing only static sources, with no
constituent gluons, is not the lowest energy flux tube state. The Coulomb
energy is also measured on thermalized lattices with center vortices removed by
the de Forcrand-D'Elia procedure. We find that when vortices are removed, the
Coulomb string tension vanishes.Comment: 8 pages, 4 EPS figures, RevTeX4; reference adde
Manifestation of Confinement in the Gluon propagator
The gluon propagator in Landau gauge is calculated on the lattice for SU(2)
gauge theory. In particular the manifestation of confinement in the gluon
propagator is studied. Removing the confining center vortices from the
Yang-Mills ensemble leads to a drastic reduction of the gluonic form factor in
the intermediate momentum regime.Comment: 3 pages, 1 figure, talk presented by H. Reinhardt at the 19th
International Symposium on Lattice Field Theory (LATTICE2001), Berlin,
19.-24.8.2001, to appear in the proceeding
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