25,475 research outputs found

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

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    Using a multicanonical Metropolis algorithm we have performed Monte Carlo simulations of the 3D 3-state Potts model on L3L^3 lattices with L=20, 30, 40, 50. Covering a range of inverse temperatures from βmin=0\beta_{\min}=0 to βmax=0.33\beta_{\max}=0.33 we calculated the infinite volume limit of the entropy density s(β)s(\beta) with its normalization obtained from s(0)=ln3s(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

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    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 ±J\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

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    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

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    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

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    For compact U(1) lattice gauge theory (LGT) we have performed a finite size scaling analysis on NτNs3N_{\tau} N_s^3 lattices for NτN_{\tau} fixed by extrapolating spatial volumes of size Ns18N_s\le 18 to NsN_s\to\infty. Within the numerical accuracy of the thus obtained fits we find for Nτ=4N_{\tau}=4, 5 and~6 second order critical exponents, which exhibit no obvious NτN_{\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

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    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

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    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

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    To investigate order-order interfaces, we perform multimagnetical Monte Carlo simulations of the 2D2D and 3D3D Ising model. Stringent tests of the numerical methods are performed by reproducing with high precision exact 2D2D results. In the physically more interesting 3D3D case we estimate the amplitude F0sF^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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