25,475 research outputs found

### Normalized entropy density of the 3D 3-state Potts model

Using a multicanonical Metropolis algorithm we have performed Monte Carlo
simulations of the 3D 3-state Potts model on $L^3$ lattices with L=20, 30, 40,
50. Covering a range of inverse temperatures from $\beta_{\min}=0$ to
$\beta_{\max}=0.33$ we calculated the infinite volume limit of the entropy
density $s(\beta)$ with its normalization obtained from $s(0)=\ln 3$. At the
transition temperature the entropy and energy endpoints in the ordered and
disordered phase are estimated employing a novel reweighting procedure. We also
evaluate the transition temperature and the order-disorder interface tension.
The latter estimate increases when capillary waves are taken into account.Comment: 5 pages, 4 figure

### Exchange Monte Carlo Method and Application to Spin Glass Simulations

We propose an efficient Monte Carlo algorithm for simulating a
``hardly-relaxing" system, in which many replicas with different temperatures
are simultaneously simulated and a virtual process exchanging configurations of
these replica is introduced. This exchange process is expected to let the
system at low temperatures escape from a local minimum. By using this algorithm
the three-dimensional $\pm J$ Ising spin glass model is studied. The ergodicity
time in this method is found much smaller than that of the multi-canonical
method. In particular the time correlation function almost follows an
exponential decay whose relaxation time is comparable to the ergodicity time at
low temperatures. It suggests that the system relaxes very rapidly through the
exchange process even in the low temperature phase.Comment: 10 pages + uuencoded 5 Postscript figures, REVTe

### Multicanonical Recursions

The problem of calculating multicanonical parameters recursively is
discussed. I describe in detail a computational implementation which has worked
reasonably well in practice.Comment: 23 pages, latex, 4 postscript figures included (uuencoded
Z-compressed .tar file created by uufiles), figure file corrected

### Form Factors in Off--Critical Superconformal Models

We discuss the determination of the lowest Form Factors relative to the trace
operators of N=1 Super Sinh-Gordon Model. Analytic continuations of these Form
Factors as functions of the coupling constant allows us to study a series of
models in a uniform way, among these the latest model of the Roaming Series and
a class of minimal supersymmetric models.Comment: 11 pages, 2 Postscript figures. To appear in the Proceedings of the
Euroconference on New Symmetries in Statistical Mech. and Cond. Mat. Physics,
Torino, July 20- August 1 199

### Non-Perturbative U(1) Gauge Theory at Finite Temperature

For compact U(1) lattice gauge theory (LGT) we have performed a finite size
scaling analysis on $N_{\tau} N_s^3$ lattices for $N_{\tau}$ fixed by
extrapolating spatial volumes of size $N_s\le 18$ to $N_s\to\infty$. Within the
numerical accuracy of the thus obtained fits we find for $N_{\tau}=4$, 5 and~6
second order critical exponents, which exhibit no obvious $N_{\tau}$
dependence. The exponents are consistent with 3d Gaussian values, but not with
either first order transitions or the universality class of the 3d XY model. As
the 3d Gaussian fixed point is known to be unstable, the scenario of a yet
unidentified non-trivial fixed point close to the 3d Gaussian emerges as one of
the possible explanations.Comment: Extended version after referee reports. 6 pages, 6 figure

### Biased Metropolis-Heat-Bath Algorithm for Fundamental-Adjoint SU(2) Lattice Gauge Theory

For SU(2) lattice gauge theory with the fundamental-adjoint action an
efficient heat-bath algorithm is not known so that one had to rely on
Metropolis simulations supplemented by overrelaxation. Implementing a novel
biased Metropolis-heat-bath algorithm for this model, we find improvement
factors in the range 1.45 to 2.06 over conventionally optimized Metropolis
simulations. If one optimizes further with respect to additional overrelaxation
sweeps, the improvement factors are found in the range 1.3 to 1.8.Comment: 4 pages, 2 figures; minor changes and one reference added; accepted
for publication in PR

### Density of states and Fisher's zeros in compact U(1) pure gauge theory

We present high-accuracy calculations of the density of states using
multicanonical methods for lattice gauge theory with a compact gauge group U(1)
on 4^4, 6^4 and 8^4 lattices. We show that the results are consistent with weak
and strong coupling expansions. We present methods based on Chebyshev
interpolations and Cauchy theorem to find the (Fisher's) zeros of the partition
function in the complex beta=1/g^2 plane. The results are consistent with
reweighting methods whenever the latter are accurate. We discuss the volume
dependence of the imaginary part of the Fisher's zeros, the width and depth of
the plaquette distribution at the value of beta where the two peaks have equal
height. We discuss strategies to discriminate between first and second order
transitions and explore them with data at larger volume but lower statistics.
Higher statistics and even larger lattices are necessary to draw strong
conclusions regarding the order of the transition.Comment: 14 pages, 16 figure

### Recent Results of Multimagnetical Simulations of the Ising Model

To investigate order-order interfaces, we perform multimagnetical Monte Carlo
simulations of the $2D$ and $3D$ Ising model. Stringent tests of the numerical
methods are performed by reproducing with high precision exact $2D$ results. In
the physically more interesting $3D$ case we estimate the amplitude $F^s_0$ of
the critical interfacial tension.Comment: talk presented at the workshop "Dynamics of First Order Phase
Transitions", Juelich June 1-3; FSU-SCRI-92C-87 preprint; 7 pages; sorry no
figures; needs vanilla.st

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