1,676 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
Spectral sum for the color-Coulomb potential in SU(3) Coulomb gauge lattice Yang-Mills theory
We discuss the essential role of the low-lying eigenmodes of the
Faddeev-Popov (FP) ghost operator on the confining color-Coulomb potential
using SU(3) quenched lattice simulations in the Coulomb gauge. The
color-Coulomb potential is expressed as a spectral sum of the FP ghost operator
and has been explored by partially summing the FP eigenmodes. We take into
account the Gribov copy effects that have a great impact on the FP eigenvalues
and the color-Coulomb potential. We observe that the lowest eigenvalue vanishes
in the thermodynamic limit much faster than that in the Landau gauge. The
color-Coulomb potential at large distances is governed by the near-zero FP
eigenmodes; in particular, the lowest one accounts for a substantial portion of
the color-Coulomb string tension comparable to the Wilson string tension.Comment: 14 pages, 14 figure
Magnetic Monopoles, Center Vortices, Confinement and Topology of Gauge Fields
The vortex picture of confinement is studied. The deconfinement phase
transition is explained as a transition from a phase in which vortices
percolate to a phase of small vortices. Lattice results are presented in
support of this scenario. Furthermore the topological properties of magnetic
monopoles and center vortices arising, respectively, in Abelian and center
gauges are studied in continuum Yang-Mills-theory. For this purpose the
continuum analog of the maximum center gauge is constructed.Comment: talk given by H. Reinhardt on the Int. Workshop ``Hadrons 1999'',
Coimbra, 10.-15. Sept. 199
Coulomb gauge gluon propagator and the Gribov formula
We analyze the lattice SU(2) Yang-Mills theory in Coulomb gauge. We show that
the static gluon propagator is multiplicative renormalizable and takes the
simple form , proposed by
Gribov through heuristic arguments many years ago. We find .Comment: 10 pages, 2 figures. Slight change of notations, some point
clarified. To appear on Phys. Rev. Let
Fermion Energies in the Background of a Cosmic String
We provide a thorough exposition, including technical and numerical details,
of previously published results on the quantum stabilization of cosmic strings.
Stabilization occurs through the coupling to a heavy fermion doublet in a
reduced version of the standard model. We combine the vacuum polarization
energy of fermion zero-point fluctuations and the binding energy of occupied
energy levels, which are of the same order in a semi-classical expansion.
Populating these bound states assigns a charge to the string. We show that
strings carrying fermion charge become stable if the electro-weak bosons are
coupled to a fermion that is less than twice as heavy as the top quark. The
vacuum remains stable in our model, because neutral strings are not
energetically favored. These findings suggests that extraordinarily large
fermion masses or unrealistic couplings are not required to bind a cosmic
string in the standard model.Comment: 38 pages, 6 figures, version accepted for publication in Phys Rev
Magnetic Monopoles, Center Vortices and Topology of Gauge Fields
The topological properties of magnetic monopoles and center vortices arising,
respectively, in Abelian and center gauges are studied in continuum Yang-Mills
Theory. For this purpose the continuum analog of the maximum center gauge is
constructed.Comment: talk presented at LATTICE99(topology) at Pisa, Italy, 3 page
A general solution in the Newtonian limit of f(R)- gravity
We show that any analytic -gravity model, in the metric approach,
presents a weak field limit where the standard Newtonian potential is corrected
by a Yukawa-like term. This general result has never been pointed out but often
derived for some particular theories. This means that only allows to
recover the standard Newton potential while this is not the case for other
relativistic theories of gravity. Some considerations on the physical
consequences of such a general solution are addressed.Comment: 5 page
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