4,089 research outputs found
On the quality of random number generators with taps
Recent exact analytical results developed for the random number generators
with taps are reported. These results are applicable to a wide class of
algorithms, including random walks, cluster algorithms, Ising models. Practical
considerations on the improvement of the quality of random numbers are
discussed as well.Comment: Conference on Computational Physics, Granada, Spain, 199
Nonlinear Inflaton Fragmentation after Preheating
We consider the nonlinear dynamics of inflaton fragmentation during and after
preheating in the simplest model of chaotic inflation. While the earlier regime
of parametric resonant particle production and the later turbulent regime of
interacting fields evolving towards equilibrium are well identified and
understood, the short intermediate stage of violent nonlinear dynamics remains
less explored. Lattice simulations of fully nonlinear preheating dynamics show
specific features of this intermediate stage: occupation numbers of the scalar
particles are peaked, scalar fields become significantly non-gaussian and the
field dynamics become chaotic and irreversible. Visualization of the field
dynamics in configuration space reveals that nonlinear interactions generate
non-gaussian inflaton inhomogeneities with very fast growing amplitudes. The
peaks of the inflaton inhomogeneities coincide with the peaks of the scalar
field(s) produced by parametric resonance. When the inflaton peaks reach their
maxima, they stop growing and begin to expand. The subsequent dynamics is
determined by expansion and superposition of the scalar waves originating from
the peaks. Multiple wave superposition results in phase mixing and turbulent
wave dynamics. Thus, the short intermediate stage is defined by the formation,
expansion and collision of bubble-like field inhomogeneities associated with
the peaks of the original gaussian field. This process is qualitatively similar
to the bubble-like inflaton fragmentation that occurs during tachyonic
preheating after hybrid or new inflation.Comment: 9 pages, 6 fig
Critical amplitude ratios of the Baxter-Wu model
A Monte Carlo simulation study of the critical and off-critical behavior of
the Baxter-Wu model, which belongs to the universality class of the 4-state
Potts model, was performed. We estimate the critical temperature window using
known analytical results for the specific heat and magnetization. This helps us
to extract reliable values of universal combinations of critical amplitudes
with reasonable accuracy. Comparisons with approximate analytical predictions
and other numerical results are discussed.Comment: 13 pages, 13 figure
Test of multiscaling in DLA model using an off-lattice killing-free algorithm
We test the multiscaling issue of DLA clusters using a modified algorithm.
This algorithm eliminates killing the particles at the death circle. Instead,
we return them to the birth circle at a random relative angle taken from the
evaluated distribution. In addition, we use a two-level hierarchical memory
model that allows using large steps in conjunction with an off-lattice
realization of the model. Our algorithm still seems to stay in the framework of
the original DLA model. We present an accurate estimate of the fractal
dimensions based on the data for a hundred clusters with 50 million particles
each. We find that multiscaling cannot be ruled out. We also find that the
fractal dimension is a weak self-averaging quantity. In addition, the fractal
dimension, if calculated using the harmonic measure, is a nonmonotonic function
of the cluster radius. We argue that the controversies in the data
interpretation can be due to the weak self-averaging and the influence of
intrinsic noise.Comment: 8 pages, 9 figure
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