218 research outputs found
SO(3) vortices and disorder in the 2d SU(2) chiral model
We study the correlation function of the 2d SU(2) principal chiral model on
the lattice. By rewriting the model in terms of Z(2) degrees of freedom coupled
to SO(3) vortices we show that the vortices play a crucial role in disordering
the correlations at low temperature. Using a series of exact transformations we
prove that, if satisfied, certain inequalities between vortex correlations
imply exponential fall-off of the correlation function at arbitrarily low
temperatures. We also present some Monte Carlo evidence that these correlation
inequalities are indeed satisfied. Our method can be easily translated to the
language of 4d SU(2) gauge theory to establish the role of corresponding SO(3)
monopoles in maintaining confinement at small couplings.Comment: 13 pages LaTe
Instanton Effects in Hadron Spectroscopy Revisited
We use an optimised clover action to study spectroscopy on an instanton
ensemble reconstructed from smoothed Monte Carlo configurations. Due to the
better chirality of the clover action, the artificial configurations show a
marked difference from the free field behaviour obtained with the Wilson
action. They however still fail to reproduce the physics observed on the
smoothed configurations. The presence of freely propagating quark modes is
found to be responsible for this.Comment: 3 pages, LaTeX with 4 eps figures, LATTICE99(topology
Vortices and the SU(3) string tension
We present simulation results comparing the SU(3) heavy quark potential
extracted from the full Wilson loop expectation to that extracted from the
expectation of the Wilson loop fluctuation solely by elements of Z(3). The two
potentials are found to coincide. This agreement is stable under multiple
smoothings of the configurations which remove short distance fluctuations, and
thus reflects long-distance physics. It strongly indicates that the asymptotic
string tension arises from thick center vortices linking with the Wilson loop.Comment: 8 pages, LaTeX file with 6 eps figure
Anderson Localization in Quark-Gluon Plasma
At low temperature the low end of the QCD Dirac spectrum is well described by
chiral random matrix theory. In contrast, at high temperature there is no
similar statistical description of the spectrum. We show that at high
temperature the lowest part of the spectrum consists of a band of statistically
uncorrelated eigenvalues obeying essentially Poisson statistics and the
corresponding eigenvectors are extremely localized. Going up in the spectrum
the spectral density rapidly increases and the eigenvectors become more and
more delocalized. At the same time the spectral statistics gradually crosses
over to the bulk statistics expected from the corresponding random matrix
ensemble. This phenomenon is reminiscent of Anderson localization in disordered
conductors. Our findings are based on staggered Dirac spectra in quenched SU(2)
lattice simulations.Comment: 11 pages, 8 figure
Monopoles and instantons in SU(2) lattice gauge theory
We investigate the monopole-instanton correlation in SU(2) lattice gauge
theory using a renormalisation group inspired smoothing technique. We look at
the properties of monopole clusters and their correlation with instantons.
Since the action of the smoothed configurations is dominated by instantons we
compare the smoothed Monte Carlo lattices to artificially reconstructed
configurations with the same instanton content but no other fluctuations. Both
parallel and randomly rotated (in group space) instanton ensembles are
considered.Comment: LATTICE98(confine
Unquenching the topological susceptibility with an overlap action
We estimate the quark-mass dependence of the topological susceptibility with
dynamical overlap and clover fermions. Unquenching effects on the
susceptibility turn out to be well approximated by a reweighting of a quenched
ensemble with a low-eigenmode truncation of the fermionic determinant. We find
that it is most likely due to the explicit chiral symmetry breaking of the
fermion action that present day dynamical simulations do not show the expected
suppression of the topological susceptibility.Comment: 3 pages, LaTeX with 3 eps figures, Lattice2001(confinement
Bound on the string tension by the excitation probability for a vortex
A lower bound on the string tension for large beta in SU(2) LGT is derived.
The derivation is from first principles and bounds the string tension from
below by the expectation for the excitation of a single `tagged' thick vortex
winding around the lattice. Thus confinement follows if this expectation
remains nonvanishing at large beta. Numerical simulations are presented to show
that this is indeed the case.Comment: LATTICE99(confine), 3 pages, 3 epsf figures, LaTeX, espcrc2.st
Poisson to Random Matrix Transition in the QCD Dirac Spectrum
At zero temperature the lowest part of the spectrum of the QCD Dirac operator
is known to consist of delocalized modes that are described by random matrix
statistics. In the present paper we show that the nature of these eigenmodes
changes drastically when the system is driven through the finite temperature
cross-over. The lowest Dirac modes that are delocalized at low temperature
become localized on the scale of the inverse temperature. At the same time the
spectral statistics changes from random matrix to Poisson statistics. We
demonstrate this with lattice QCD simulations using 2+1 flavors of light
dynamical quarks with physical masses. Drawing an analogy with Anderson
transitions we also examine the mobility edge separating localized and
delocalized modes in the spectrum. We show that it scales in the continuum
limit and increases sharply with the temperature.Comment: 10 pages, 9 eps figures, a few references added and typos correcte
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