612 research outputs found
Probing the QCD Vacuum with Static Sources in Maximal Abelian Projection
Various field strength correlators are investigated in the maximal Abelian
projection of pure SU(2) lattice gauge theory. High precision measurements of
the colour fields, monopole currents, their curls and divergences allow for
detailed checks of the dual superconductor scenario. On this basis, we perform
a Ginzburg-Landau type analysis of the flux tube profile from which we derive
the size of the penetration length, LAMBDA = 0.16(2) fm, and coherence length
of the monopole condensate wave function, XI = 0.27(3) fm. The ratio of these
numbers is KAPPA = LAMBDA/XI = 0.59(13) which is below the value 1/SQRT(2)
where type II superconductivity sets in.Comment: 15 pages, latex, 8 figures, Talk presented by K. Schilling YKIS97,
Kyot
Many Masses on One Stroke: Economic Computation of Quark Propagators
The computational effort in the calculation of Wilson fermion quark
propagators in Lattice Quantum Chromodynamics can be considerably reduced by
exploiting the Wilson fermion matrix structure in inversion algorithms based on
the non-symmetric Lanczos process. We consider two such methods: QMR (quasi
minimal residual) and BCG (biconjugate gradients). Based on the decomposition
of the Wilson mass matrix, using QMR, one can carry
out inversions on a {\em whole} trajectory of masses simultaneously, merely at
the computational expense of a single propagator computation. In other words,
one has to compute the propagator corresponding to the lightest mass only,
while all the heavier masses are given for free, at the price of extra storage.
Moreover, the symmetry can be used to cut
the computational effort in QMR and BCG by a factor of two. We show that both
methods then become---in the critical regime of small quark
masses---competitive to BiCGStab and significantly better than the standard MR
method, with optimal relaxation factor, and CG as applied to the normal
equations.Comment: 17 pages, uuencoded compressed postscrip
Anatomy of String Breaking in QCD
We investigate the string breaking mechanism in n_f=2 QCD. We discuss the
lattice techniques used and present results on energy levels and mixing angle
of the static BBbar|QbarQ two-state system. The string breaking is visualized,
by means of an animation of the action density distribution as a function of
the static colour source-antisource separation.Comment: Talk presented at Lattice 2005 (Topology and Confinement), Dublin,
July 25-30, 2005; 6 pages, 5 figures, 2 mpeg animations not included because
of file size problems but href linked, uses PoS.cls; to appear in Proceedings
of Scienc
Finite size scaling analysis of compact QED
We describe results of a high-statistics finite size scaling analysis of 4d
compact U(1) lattice gauge theory with Wilson action at the phase transition
point. Using a multicanonical hybrid Monte Carlo algorithm we generate data
samples with more than 150 tunneling events between the metastable states of
the system, on lattice sizes up to 18^4. We performed a first analysis within
the Borgs-Kotecky finite size scaling scheme. As a result, we report evidence
for a first-order phase transition with a plaquette energy gap, G=0.02667(20),
at a transition coupling, beta_T=1.011128(11).Comment: Lattice 2000 (Topics in Gauge Theories),6 pages, 6 figures, LaTe
Spatial Besov Regularity for Stochastic Partial Differential Equations on Lipschitz Domains
We use the scale of Besov spaces B^\alpha_{\tau,\tau}(O), \alpha>0,
1/\tau=\alpha/d+1/p, p fixed, to study the spatial regularity of the solutions
of linear parabolic stochastic partial differential equations on bounded
Lipschitz domains O\subset R^d. The Besov smoothness determines the order of
convergence that can be achieved by nonlinear approximation schemes. The proofs
are based on a combination of weighted Sobolev estimates and characterizations
of Besov spaces by wavelet expansions.Comment: 32 pages, 3 figure
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