424 research outputs found
Nonequilibrium Precursor Model for the Onset of Percolation in a Two-Phase System
Using a Boltzmann equation, we investigate the nonequilibrium dynamics of
nonperturbative fluctuations within the context of Ginzburg-Landau models. As
an illustration, we examine how a two-phase system initially prepared in a
homogeneous, low-temperature phase becomes populated by precursors of the
opposite phase as the temperature is increased. We compute the critical value
of the order parameter for the onset of percolation, which signals the
breakdown of the conventional dilute gas approximation.Comment: 4 pages, 4 eps figures (uses epsf), Revtex. Replaced with version in
press Physical Review
Domain growth within the backbone of the three-dimensional Edwards-Anderson spin glass
The goal of this work is to show that a ferromagnetic-like domain growth
process takes place within the backbone of the three-dimensional
Edwards-Anderson (EA) spin glass model. To sustain this affirmation we study
the heterogeneities displayed in the out-of-equilibrium dynamics of the model.
We show that both correlation function and mean flipping time distribution
present features that have a direct relation with spatial heterogeneities, and
that they can be characterized by the backbone structure. In order to gain
intuition we analyze the pure ferromagnetic Ising model, where we show the
presence of dynamical heterogeneities in the mean flipping time distribution
that are directly associated to ferromagnetic growing domains. We extend a
method devised to detect domain walls in the Ising model to carry out a similar
analysis in the three-dimensional EA spin glass model. This allows us to show
that there exists a domain growth process within the backbone of this model.Comment: 10 pages, 10 figure
Nonequilibrium dynamics of the three-dimensional Edwards-Anderson spin-glass model with Gaussian couplings: Strong heterogeneities and the backbone picture
We numerically study the three-dimensional Edwards-Anderson model with
Gaussian couplings, focusing on the heterogeneities arising in its
nonequilibrium dynamics. Results are analyzed in terms of the backbone picture,
which links strong dynamical heterogeneities to spatial heterogeneities
emerging from the correlation of local rigidity of the bond network. Different
two-times quantities as the flipping time distribution and the correlation and
response functions, are evaluated over the full system and over high- and
low-rigidity regions. We find that the nonequilibrium dynamics of the model is
highly correlated to spatial heterogeneities. Also, we observe a similar
physical behavior to that previously found in the Edwards-Anderson model with a
bimodal (discrete) bond distribution. Namely, the backbone behaves as the main
structure that supports the spin-glass phase, within which a sort of
domain-growth process develops, while the complement remains in a paramagnetic
phase, even below the critical temperature
Perturbative evolution of the static configurations, quasinormal modes and quasi normal ringing in the Apostolatos - Thorne cylindrical shell model
We study the perturbative evolution of the static configurations, quasinormal
modes and quasi normal ringing in the Apostolatos - Thorne cylindrical shell
model. We consider first an expansion in harmonic modes and show that it
provides a complete solution for the characteristic value problem for the
finite perturbations of a static configuration. As a consequence of this
completeness we obtain a proof of the stability of static solutions under this
type of perturbations. The explicit expression for the mode expansion are then
used to obtain numerical values for some of the quasi normal mode complex
frequencies. Some examples involving the numerical evaluation of the integral
mode expansions are described and analyzed, and the quasi normal ringing
displayed by the solutions is found to be in agreement with quasi normal modes
found previously. Going back to the full relativistic equations of motion we
find their general linear form by expanding to first order about a static
solution. We then show that the resulting set of coupled ordinary and partial
differential equations for the dynamical variables of the system can be used to
set an initial plus boundary values problem, and prove that there is an
associated positive definite constant of the motion that puts absolute bounds
on the dynamic variables of the system, establishing the stability of the
motion of the shell under arbitrary, finite perturbations. We also show that
the problem can be solved numerically, and provide some explicit examples that
display the complete agreement between the purely numerical evolution and that
obtained using the mode expansion, in particular regarding the quasi normal
ringing that results in the evolution of the system. We also discuss the
relation of the present work to some recent results on the same model that have
appeared in the literature.Comment: 27 pages, 7 figure
Dynamics of Weak First Order Phase Transitions
The dynamics of weak vs. strong first order phase transitions is investigated
numerically for 2+1 dimensional scalar field models. It is argued that the
change from a weak to a strong transition is itself a (second order) phase
transition, with the order parameter being the equilibrium fractional
population difference between the two phases at the critical temperature, and
the control parameter being the coefficient of the cubic coupling in the
free-energy density. The critical point is identified, and a power law
controlling the relaxation dynamics at this point is obtained. Possible
applications are briefly discussed.Comment: 11 pages, 4 figures in uuencoded compressed file (see instructions in
main text), RevTeX, DART-HEP-94/0
The collision of boosted black holes: second order close limit calculations
We study the head-on collision of black holes starting from unsymmetrized,
Brill--Lindquist type data for black holes with non-vanishing initial linear
momentum. Evolution of the initial data is carried out with the ``close limit
approximation,'' in which small initial separation and momentum are assumed,
and second-order perturbation theory is used. We find agreement that is
remarkably good, and that in some ways improves with increasing momentum. This
work extends a previous study in which second order perturbation calculations
were used for momentarily stationary initial data, and another study in which
linearized perturbation theory was used for initially moving holes. In addition
to supplying answers about the collisions, the present work has revealed
several subtle points about the use of higher order perturbation theory, points
that did not arise in the previous studies. These points include issues of
normalization, and of comparison with numerical simulations, and will be
important to subsequent applications of approximation methods for collisions.Comment: 20 pages, RevTeX, 6 figures included with psfi
Non-perturbative effects in a rapidly expanding quark-gluon plasma
Within first-order phase transitions, we investigate the pre-transitional
effects due to the nonperturbative, large-amplitude thermal fluctuations which
can promote phase mixing before the critical temperature is reached from above.
In contrast with the cosmological quark-hadron transition, we find that the
rapid cooling typical of the RHIC and LHC experiments and the fact that the
quark-gluon plasma is chemically unsaturated suppress the role of
non-perturbative effects at current collider energies. Significant supercooling
is possible in a (nearly) homogeneous state of quark gluon plasma.Comment: LaTeX, 7 pages with 7 Postscript figures. Figures added, discussions
added. Version to appear in Phys. Rev.
Dynamical heterogeneities as fingerprints of a backbone structure in Potts models
We investigate slow non-equilibrium dynamical processes in two-dimensional
--state Potts model with both ferromagnetic and couplings. Dynamical
properties are characterized by means of the mean-flipping time distribution.
This quantity is known for clearly unveiling dynamical heterogeneities. Using a
two-times protocol we characterize the different time scales observed and
relate them to growth processes occurring in the system. In particular we
target the possible relation between the different time scales and the spatial
heterogeneities originated in the ground state topology, which are associated
to the presence of a backbone structure. We perform numerical simulations using
an approach based on graphics processing units (GPUs) which permits to reach
large system sizes. We present evidence supporting both the idea of a growing
process in the preasymptotic regime of the glassy phases and the existence of a
backbone structure behind this processes.Comment: 9 pages, 7 figures, Accepted for publication in PR
- …