1,768 research outputs found
On the temporal Wilson loop in the Hamiltonian approach in Coulomb gauge
We investigate the temporal Wilson loop using the Hamiltonian approach to
Yang-Mills theory. In simple cases such as the Abelian theory or the
non-Abelian theory in (1+1) dimensions, the known results can be reproduced
using unitary transformations to take care of time evolution. We show how
Coulomb gauge can be used for an alternative solution if the exact ground state
wave functional is known. In the most interesting case of Yang-Mills theory in
(3+1) dimensions, the vacuum wave functional is not known, but recent
variational approaches in Coulomb gauge give a decent approximation. We use
this formulation to compute the temporal Wilson loop and find that the Wilson
and Coulomb string tension agree within our approximation scheme. Possible
improvements of these findings are briefly discussed.Comment: 24 pages, 4 eps-figures; new version matches published on
The role of center vortices in Gribov's confinement scenario
The connection of Gribov's confinement scenario in Coulomb gauge with the
center vortex picture of confinement is investigated. For this purpose we
assume a vacuum wave functional which models the infrared properties of the
theory and in particular shows strict confinement, i.e. an area law of the
Wilson loop. We isolate the center vortex content of this wave functional by
standard lattice methods and investigate their contributions to various static
propagators of the Hamilton approach to Yang-Mills theory in Coulomb gauge. We
find that the infrared properties of these quantities, in particular the
infrared divergence of the ghost form factor, are dominated by center vortices.Comment: 18 pages, 5 figure
Ghost propagator and the Coulomb form factor from the lattice
We calculate the Coulomb ghost propagator G(|p|) and the static Coulomb
potential V_C(|r|) for SU(2) Yang-Mills theory on the lattice. In view of
possible scaling violations related to deviations from the Hamiltonian limit we
use anisotropic lattices to improve the temporal resolution. We find that the
ghost propagator is infrared enhanced with an exponent kappa_gh ~ 0.5 while the
Coulomb potential exhibits a string tension larger than the Wilson string
tension, sigma_C ~ 2 sigma. This agrees with the Coulomb "scaling" scenario
derived from the Gribov-Zwanziger confinement mechanism.Comment: 23 pages, 5 figures. Some issues clarified and extended, references
added. To appear in PR
Coulomb Confinement from the Yang-Mills Vacuum State in 2+1 Dimensions
The Coulomb-gauge ghost propagator, and the color-Coulomb potential, are
computed in an ensemble of configurations derived from our recently proposed
Yang-Mills vacuum wavefunctional in 2+1 dimensions. The results are compared to
the corresponding values obtained by standard Monte Carlo simulations in three
Euclidean dimensions. The agreement is quite striking for the Coulomb-gauge
ghost propagator. The color-Coulomb potential rises linearly at large
distances, but its determination suffers from rather large statistical
fluctuations, due to configurations with very low values of , the lowest
eigenvalue of the Coulomb-gauge Faddeev-Popov operator. However, if one imposes
cuts on the data, effectively leaving out configurations with very low ,
the agreement of the potential in both sets of configurations is again
satisfactory, although the errorbars grow systematically as the cutoff is
eliminated.Comment: 8 pages, 5 figures (10 EPS files), RevTeX4.1. V2: original figs. 4
and 5 compressed into a new fig. 5; a new fig. 4; sec. IV.B slightly modified
to reflect the changes. Version to appear in Phys. Rev. D. V3: a reference
corrected
Stable charged cosmic strings
We study the quantum stabilization of a cosmic string by a heavy fermion
doublet in a reduced version of the standard model. We show that charged
strings, obtained by populating fermionic bound state levels, become stable if
the electro--weak bosons are coupled to a fermion that is less than twice as
heavy as the top quark. This result suggests that extraordinarily large fermion
masses or unrealistic couplings are not required to bind a cosmic string in the
standard model. Numerically we find the most favorable string profile to be a
simple "trough" in the Higgs vev of radius . The
vacuum remains stable in our model, because neutral strings are not
energetically favored.Comment: 5 pages, 3 figures, version to be published in Phys. Rev. Let
Attractive Electromagnetic Casimir Stress on a Spherical Dielectric Shell
Based on calculations involving an idealized boundary condition, it has long
been assumed that the stress on a spherical conducting shell is repulsive. We
use the more realistic case of a Drude dielectric to show that the stress is
attractive, matching the generic behavior of Casimir forces in
electromagnetism. We trace the discrepancy between these two cases to
interactions between the electromagnetic quantum fluctuations and the
dielectric material.Comment: Five pages, one figure, pdflatex, matches version to be pusblished in
Phys Lett
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