486 research outputs found
The decay of unstable k-strings in SU(N) gauge theories at zero and finite temperature
Sources in higher representations of SU(N) gauge theory at T=0 couple with
apparently stable strings with tensions depending on the specific
representation rather than on its N-ality. Similarly at the deconfining
temperature these sources carry their own representation-dependent critical
exponents. It is pointed out that in some instances one can evaluate exactly
these exponents by fully exploiting the correspondence between the 2+1
dimensional critical gauge theory and the 2d conformal field theory in the same
universality class. The emerging functional form of the Polyakov-line
correlators suggests a similar form for Wilson loops in higher representations
which helps in understanding the behaviour of unstable strings at T=0. A
generalised Wilson loop in which along part of its trajectory a source is
converted in a gauge invariant way into higher representations with same
N-ality could be used as a tool to estimate the decay scale of the unstable
strings.Comment: 18 pages, 4 figures v2: typos correcte
Topological susceptibility of SU(N) gauge theories at finite temperature
We investigate the large-N behavior of the topological susceptibility in
four-dimensional SU(N) gauge theories at finite temperature, and in particular
across the finite-temperature transition at Tc. For this purpose, we consider
the lattice formulation of the SU(N) gauge theories and perform Monte Carlo
simulations for N=4,6. The results indicate that the topological susceptibility
has a nonvanishing large-N limit for T<Tc, as at T=0, and that the topological
properties remain substantially unchanged in the low-temperature phase. On the
other hand, above the deconfinement phase transition, the topological
susceptibility shows a large suppression. The comparison between the data for
N=4 and N=6 hints at a vanishing large-N limit for T>Tc.Comment: 9 pages, 2 figs, a few discussions added, JHEP in pres
SU(3) vortex-like configurations in the maximal center gauge
A new algorithm for fixing the gauge to (direct) maximal center gauge in
SU(N) lattice gauge theory is presented. We check how this method works on
SU(3) configurations which are vortex-like, and show how these configurations
look like when center projected.Comment: LATTICE99(confine)-3p,5 postscript figure
Study of SU(3) vortex-like configurations with a new maximal center gauge fixing method
We present a new way of fixing the gauge to (direct) maximal center gauge in
SU(N) Yang-Mills theory and apply this method to SU(3) configurations which are
vortex-like. We study the structure of the Z_3 configurations obtained after
center-projecting the SU(3) ones.Comment: 11 pages, 2 figures. To appear in PL
Center vortices on SU(2) lattices
We show that gauge invariant definition of thin, thick and hybrid center
vortices, defined by Kovacs and Tomboulis on SO(3) x Z(2) configurations, can
also be defined in SU(2). We make this connection using the freedom of choosing
a particular SU(2) representative of SO(3). We further show that in another
representative the Tomboulis \sigma - \eta thin vortices are P (projection)
vortices. The projection approximation corresponds to dropping the perimeter
factor of a Wilson loop after appropriate gauge fixing. We present results for
static quark potentials based on these vortex counters and compare pojection
vortex counters with gauge invariant ones on the same configuration.Comment: LaTe
Numerical computation of the beta function of large N SU(N) gauge theory coupled to an adjoint Dirac fermion
We use a single site lattice in four dimensions to study the scaling of large
N Yang-Mills field coupled to a single massless Dirac fermion in the adjoint
representation. We use the location of the strong to weak coupling transition
defined through the eigenvalues of the folded Wilson loop operator to set a
scale. We do not observe perturbative scaling in the region studied in this
paper. Instead, we observe that the scale changes very slowly with the bare
coupling. The lowest eigenvalue of the overlap Dirac operator is another scale
that shows similar behavior as a function of the lattice coupling. We speculate
that this behavior is due to the beta function appoaching close to a zero.Comment: 16 pages, 9 figures, revised version DOES NOT match the published
version in Physical Review
Local coherence and deflation of the low quark modes in lattice QCD
The spontaneous breaking of chiral symmetry in QCD is known to be linked to a
non-zero density of eigenvalues of the massless Dirac operator near the origin.
Numerical studies of two-flavour QCD now suggest that the low quark modes are
locally coherent to a certain extent. As a consequence, the modes can be
simultaneously deflated, using local projectors, with a total computational
effort proportional to the lattice volume (rather than its square). Deflation
has potentially many uses in lattice QCD. The technique is here worked out for
the case of quark propagator calculations, where large speed-up factors and a
flat scaling behaviour with respect to the quark mass are achieved.Comment: Plain TeX, 23 pages, 4 figures included; minor text modifications;
version published in JHE
Magnetic charge superselection in the deconfined phase of Yang-Mills theory
The vacuum expectation value of an operator carrying magnetic charge is
studied numerically for temperatures above the deconfinement temperature in
SU(2) and SU(3) gauge theory. By analyzing its finite size behaviour, this is
found to be exactly zero in the thermodynamical limit for any T > T_c whenever
the magnetic charge of the operator is different from zero. These results show
that magnetic charge is superselected in the hot phase of quenched QCD.Comment: 4 pages, 6 figures, revtex
Color confinement and dual superconductivity in unquenched QCD
We report on evidence from lattice simulations that confinement is produced
by dual superconductivity of the vacuum in full QCD as in quenched QCD.
Preliminary information is obtained on the order of the deconfining phase
transition.Comment: 4 pages, to appear in the Proceedings of Quark Matter 02 - The XVI
International Conference on Ultrarelativistic Nucleus-Nucleus Collision
Conformal vs confining scenario in SU(2) with adjoint fermions
The masses of the lowest-lying states in the meson and in the gluonic sector
of an SU(2) gauge theory with two Dirac flavors in the adjoint representation
are measured on the lattice at a fixed value of the lattice coupling for values of the bare fermion mass that span a range
between the quenched regime and the massless limit, and for various lattice
volumes. Even for light constituent fermions the lightest glueballs are found
to be lighter than the lightest mesons. Moreover, the string tension between
two static fundamental sources strongly depends on the mass of the dynamical
fermions and becomes of the order of the inverse squared lattice linear size
before the chiral limit is reached. The implications of these findings for the
phase of the theory in the massless limit are discussed and a strategy for
discriminating between the (near--)conformal and the confining scenario is
outlined.Comment: 5 pages, 4 figures using RevTeX4, Typos corrected, references added.
Versions to appear on PR
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