742 research outputs found
Zone methods and the fermion sign problem
We review a recently proposed approach to the problem of alternating signs
for fermionic many body Monte Carlo simulations in finite temperature
simulations. We derive an estimate for fermion wandering lengths and introduce
the notion of permutation zones, special regions of the lattice where identical
fermions may interchange and outside of which they may not. Using successively
larger permutation zones, one can extrapolate to obtain thermodynamic
observables in regimes where direct simulation is impossible.Comment: 3 pages, 1 figure, Lattice2002(algor
The Solid-on-Solid Surface Width Around the Roughening Transition
We investigate the surface width of solid-on-solid surfaces in the
vicinity of the roughening temperature . Above , is expected to
diverge with the system size like . However, close to a clean
behavior can only be seen on extremely large lattices. Starting from
the Kosterlitz-Thouless renormalization group, we derive an improved formula
that describes the small behavior on both sides of . For the Discrete
Gaussian model, we used the valleys-to-mountains-reflections cluster algorithm
in order to simulate the fluctuating solid-on-solid surface. The base plane
above which the surface is defined is an square lattice. In the
simulation we took . The improved formula fits the numerical
results very well. {}From the analysis, we estimate the roughening temperature
to be .Comment: 9 pages, LaTeX (no figures), FSU-SCRI-93-67, CERN-TH.6893/9
Scaling in the two-dimensional U(1)--Higgs model
We study the continuum limit of the U(1)--Higgs model with variable
scalar field length, which is qualitatively different from the fixed length
case. Our simulations concentrate on the scaling behaviour of the topological
susceptibility, and an instanton-induced confinement mechanism of fractional
charges is numerically confirmed.Comment: Talk presented at LATTICE96(topology), 3 pages, latex2e, 2 Postscript
figures, uses packages epsfig and espcrc
Monte Carlo Renormalization Group Study of the d=1 XXZ Model
We report current progress on the synthesis of methods to alleviate two major
difficulties in implementing a Monte Carlo Renormalization Group (MCRG) for
quantum systems. In particular, we have utilized the loop-algorithm to reduce
critical slowing down, and we have implemented an MCRG method in which the
symmetries of the classical equivalent model need not be fully understood,
since the Renormalization Group is given by the Monte Carlo simulation. We
report preliminary results obtained when the resulting MCRG method is applied
to the d=1 XXZ model. Our results are encouraging. However, since this model
has a Kosterlitz-Thouless transition, it does not yet provide a full test of
our MCRG method.Comment: To appear in "Quantum Monte Carlo Methods in Condensed Matter
Physics", ed.\ M. Suzuki, World Scientific, 1993. 14 pages, LaTeX, (3 figures
available on request), FSU-SCRI-93-11
Dgsos on DTRS
We perform simulations of a discrete gaussian solid on solid (DGSOS) model on
dynamical graphs, which is equivalent to coupling the model to 2d
quantum gravity, using the cluster algorithms recently developed by Evertz
et.al.for use on fixed lattices. We find evidence from the growth of the
width-squared in the rough phase of KT-like behaviour, which is consistent with
theoretical expectations. We also investigate the cluster statistics, dynamical
critical exponent and lattice properties, and compare these with the dual XY
model.Comment: 9 pages, COLO-HEP-32
Solving the Complex Phase Problem in a QCD Related Model
We discuss an effective theory for QCD at finite chemical potential and
non-zero temperature, where QCD is reduced to its center degrees of freedom.
The effective action can be mapped to a flux representation, where the complex
phase problem is solved and the theory accessible to Monte Carlo techniques. In
this work, we use a generalized Prokof'ev-Svistunov worm algorithm to perform
the simulations and determine the phase diagram as a function of temperature,
quark mass and chemical potential. It turns out that the transition is
qualitatively as expected for QCD.Comment: 6 pages and 3 figures, proceedings for "Excited QCD", Les Houches,
France, 20 - 25 February, 201
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