740 research outputs found
Direct determination of the gauge coupling derivatives for the energy density in lattice QCD
By matching Wilson loop ratios on anisotropic lattices we measure the
coefficients \cs and \ct, which are required for the calculation of the
energy density. The results are compared to that of an indirect method of
determination. We find similar behaviour, the differences are attributed to
different discretization errors.Comment: Talk presented at LATTICE97(finite temperature), 3 pages, 5
Postscript figure
Shocks in the asymmetric exclusion process with internal degree of freedom
We determine all families of Markovian three-states lattice gases with pair
interaction and a single local conservation law. One such family of models is
an asymmetric exclusion process where particles exist in two different
nonconserved states. We derive conditions on the transition rates between the
two states such that the shock has a particularly simple structure with minimal
intrinsic shock width and random walk dynamics. We calculate the drift velocity
and diffusion coefficient of the shock.Comment: 26 pages, 1 figur
Interface Fluctuations under Shear
Coarsening systems under uniform shear display a long time regime
characterized by the presence of highly stretched and thin domains. The
question then arises whether thermal fluctuations may actually destroy this
layered structure. To address this problem in the case of non-conserved
dynamics we study an anisotropic version of the Burgers equation, constructed
to describe thermal fluctuations of an interface in the presence of a uniform
shear flow. As a result, we find that stretched domains are only marginally
stable against thermal fluctuations in , whereas they are stable in .Comment: 3 pages, shorter version, additional reference
The beta function and equation of state for QCD with two flavors of quarks
We measure the pressure and energy density of two flavor QCD in a wide range
of quark masses and temperatures. The pressure is obtained from an integral
over the average plaquette or psi-bar-psi. We measure the QCD beta function,
including the anomalous dimension of the quark mass, in new Monte Carlo
simulations and from results in the literature. We use it to find the
interaction measure, E-3p, yielding non-perturbative values for both the energy
density E and the pressure p. uuencoded compressed PostScript file Revised
version should work on more PostScript printers.Comment: 24 page
On the solvable multi-species reaction-diffusion processes
A family of one-dimensional multi-species reaction-diffusion processes on a
lattice is introduced. It is shown that these processes are exactly solvable,
provided a nonspectral matrix equation is satisfied. Some general remarks on
the solutions to this equation, and some special solutions are given. The
large-time behavior of the conditional probabilities of such systems are also
investigated.Comment: 13 pages, LaTeX2
Static avalanches and Giant stress fluctuations in Silos
We propose a simple model for arch formation in silos. We show that small
pertubations (such as the thermal expansion of the beads) may lead to giant
stress fluctuations on the bottom plate of the silo. The relative amplitude
of these fluctuations are found to be power-law distributed, as
, . These fluctuations are related to large
scale `static avalanches', which correspond to long-range redistributions of
stress paths within the silo.Comment: 10 pages, 4 figures.p
Exact solution of a one-parameter family of asymmetric exclusion processes
We define a family of asymmetric processes for particles on a one-dimensional
lattice, depending on a continuous parameter ,
interpolating between the completely asymmetric processes [1] (for ) and the n=1 drop-push models [2] (for ). For arbitrary \la,
the model describes an exclusion process, in which a particle pushes its right
neighbouring particles to the right, with rates depending on the number of
these particles. Using the Bethe ansatz, we obtain the exact solution of the
master equation .Comment: 14 pages, LaTe
Numerical study of O(a) improved Wilson quark action on anisotropic lattice
The improved Wilson quark action on the anisotropic lattice is
investigated. We carry out numerical simulations in the quenched approximation
at three values of lattice spacing (--2 GeV) with the
anisotropy , where and are
the spatial and the temporal lattice spacings, respectively. The bare
anisotropy in the quark field action is numerically tuned by the
dispersion relation of mesons so that the renormalized fermionic anisotropy
coincides with that of gauge field. This calibration of bare anisotropy is
performed to the level of 1 % statistical accuracy in the quark mass region
below the charm quark mass. The systematic uncertainty in the calibration is
estimated by comparing the results from different types of dispersion
relations, which results in 3 % on our coarsest lattice and tends to vanish in
the continuum limit. In the chiral limit, there is an additional systematic
uncertainty of 1 % from the chiral extrapolation.
Taking the central value from the result of the
calibration, we compute the light hadron spectrum. Our hadron spectrum is
consistent with the result by UKQCD Collaboration on the isotropic lattice. We
also study the response of the hadron spectrum to the change of anisotropic
parameter, . We find that the change
of by 2 % induces a change of 1 % in the spectrum for physical quark
masses. Thus the systematic uncertainty on the anisotropic lattice, as well as
the statistical one, is under control.Comment: 27 pages, 25 eps figures, LaTe
Canonical phase space approach to the noisy Burgers equation: Probability distributions
We present a canonical phase space approach to stochastic systems described
by Langevin equations driven by white noise. Mapping the associated
Fokker-Planck equation to a Hamilton-Jacobi equation in the nonperturbative
weak noise limit we invoke a {\em principle of least action} for the
determination of the probability distributions. We apply the scheme to the
noisy Burgers and KPZ equations and discuss the time-dependent and stationary
probability distributions. In one dimension we derive the long-time skew
distribution approaching the symmetric stationary Gaussian distribution. In the
short-time region we discuss heuristically the nonlinear soliton contributions
and derive an expression for the distribution in accordance with the directed
polymer-replica and asymmetric exclusion model results. We also comment on the
distribution in higher dimensions.Comment: 18 pages Revtex file, including 8 eps-figures, submitted to Phys.
Rev.
Non-universal exponents in interface growth
We report on an extensive numerical investigation of the Kardar-Parisi-Zhang
equation describing non-equilibrium interfaces. Attention is paid to the
dependence of the growth exponents on the details of the distribution of the
noise. All distributions considered are delta-correlated in space and time, and
have finite cumulants. We find that the exponents become progressively more
sensitive to details of the distribution with increasing dimensionality. We
discuss the implications of these results for the universality hypothesis.Comment: 12 pages, 5 figures; to appear in Phys. Rev. Let
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