744 research outputs found
A Monte Carlo study of the three-dimensional XY universality class:Universal amplitude ratios
We simulate lattice models in the three-dimensional XY universality class in
the low and the high temperature phase. This allows us to compute a number of
universal amplitude ratios with unprecedented precision: R_{\Upsilon}=0.411(2),
R_B=2.83(1), R_{\xi}^+=0.3562(10) and R_{\xi}^-=0.850(5). These results can be
compared with those obtained from other theoretical methods, such as field
theoretic methods or the high temperature series expansion and also with
experimental results for the lambda-transition of He. In addition to the XY
model, we study the three-dimensional two-component model on the
simple cubic lattice. The parameter of the model is chosen such that
leading corrections to scaling are small.Comment: 28 pages 5 figure
Speeding up the HMC: QCD with Clover-Improved Wilson Fermions
We apply a recent proposal to speed up the Hybrid-Monte-Carlo simulation of
systems with dynamical fermions to two flavor QCD with clover-improvement. For
our smallest quark masses we see a speed-up of more than a factor of two
compared with the standard algorithm.Comment: 3 pages, lattice2002, algorithms, DESY Report-no correcte
Rough Interfaces Beyond the Gaussian Approximation
We compare predictions of the Capillary Wave Model with Monte Carlo results
for the energy gap and the interface energy of the 3D Ising model in the
scaling region. Our study reveals that the finite size effects of these
quantities are well described by the Capillary Wave Model, expanded to two-loop
order (one order beyond the Gaussian approximation).Comment: Contribution to LATTICE 94. 3 pages, PostScript fil
Thermodynamic Casimir effect: Universality and Corrections to Scaling
We study the thermodynamic Casimir force for films in the three-dimensional
Ising universality class with symmetry breaking boundary conditions. We focus
on the effect of corrections to scaling and probe numerically the universality
of our results. In particular we check our hypothesis that corrections are well
described by an effective thickness L_{0,eff}=L_0+c (L_0+L_s)^{1-\omega} +L_s,
where c and L_s are system specific parameters and \omega\approx 0.8 is the
exponent of the leading bulk correction. We simulate the improved Blume-Capel
model and the Ising model on the simple cubic lattice. First we analyse the
behaviour of various quantities at the critical point. Taking into account
corrections \propto L_0^{-\omega} in the case of the Ising model, we find good
consistency of results obtained from these two different models. In particular
we get from the analysis of our data for the Ising model for the difference of
Casimir amplitudes \Delta_{+-}-\Delta_{++}=3.200(5), which nicely compares with
\Delta_{+-}-\Delta_{++}=3.208(5) obtained by studying the improved Blume-Capel
model. Next we study the behaviour of the thermodynamic Casimir force for large
values of the scaling variable x=t [L_0/\xi_0]. This behaviour can be obtained
up to an overall amplitude by expressing the partition function of the film in
terms of eigenvalues and eigenstates of the transfermatrix and boundary states.
Here we show how this overall amplitude can be computed with high accuracy.
Finally we discuss our results for the scaling functions \theta_{+-} and
\theta_{++} of the thermodynamic Casimir force for the whole range of the
scaling variable. We conclude that our numerical results are in accordance with
universality. Corrections to scaling are well approximated by an effective
thickness.Comment: 35 pages, 5 figures, various typos correcte
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