54 research outputs found
A Study of Activated Processes in Soft Sphere Glass
On the basis of long simulations of a binary mixture of soft spheres just
below the glass transition, we make an exploratory study of the activated
processes that contribute to the dynamics. We concentrate on statistical
measures of the size of the activated processes.Comment: 17 pages, 9 postscript figures with epsf, uses harvmac.te
Some non perturbative calculations on spin glasses
Models of spin glasses are studied with a phase transition discontinuous in
the Parisi order parameter. It is assumed that the leading order corrections to
the thermodynamic limit of the high temperature free energy are due to the
existence of a metastable saddle point in the replica formalism. An ansatz is
made on the form of the metastable point and its contribution to the free
energy is calculated. The Random Energy Model is considered along with the
p-spin and the p-state Potts Models in their p < infinity expansion.Comment: 12 pages, LaTe
A tentative Replica Study of the Glass Transition
We propose a method to study quantitatively the glass transition in a system
of interacting particles. In spite of the absence of any quenched disorder, we
introduce a replicated version of the hypernetted chain equations. The solution
of these equations, for hard or soft spheres, signals a transition to the glass
phase. However the predicted value of the energy and specific heat in the glass
phase are wrong, calling for an improvement of this method.Comment: 9 pages, four postcript figures attache
A Search for Fluctuation-Dissipation Theorem Violations in Spin-Glasses from Susceptibility Data
We propose an indirect way of studying the fluctuation-dissipation relation
in spin-glasses that only uses available susceptibility data. It is based on a
dynamic extension of the Parisi-Toulouse approximation and a Curie-Weiss
treatment of the average magnetic couplings. We present the results of the
analysis of several sets of experimental data obtained from various samples.Comment: 7 pages, 4 figure
Generic two-phase coexistence in nonequilibrium systems
Gibbs' phase rule states that two-phase coexistence of a single-component
system, characterized by an n-dimensional parameter-space, may occur in an
n-1-dimensional region. For example, the two equilibrium phases of the Ising
model coexist on a line in the temperature-magnetic-field phase diagram.
Nonequilibrium systems may violate this rule and several models, where phase
coexistence occurs over a finite (n-dimensional) region of the parameter space,
have been reported. The first example of this behaviour was found in Toom's
model [Toom,Geoff,GG], that exhibits generic bistability, i.e. two-phase
coexistence over a finite region of its two-dimensional parameter space (see
Section 1). In addition to its interest as a genuine nonequilibrium property,
generic multistability, defined as a generalization of bistability, is both of
practical and theoretical relevance. In particular, it has been used recently
to argue that some complex structures appearing in nature could be truly stable
rather than metastable (with important applications in theoretical biology),
and as the theoretical basis for an error-correction method in computer science
(see [GG,Gacs] for an illuminating and pedagogical discussion of these ideas).Comment: 7 pages, 6 figures, to appear in Eur. Phys. J. B, svjour.cls and
svepj.clo neede
Power-law running of the effective gluon mass
The dynamically generated effective gluon mass is known to depend
non-trivially on the momentum, decreasing sufficiently fast in the deep
ultraviolet, in order for the renormalizability of QCD to be preserved. General
arguments based on the analogy with the constituent quark masses, as well as
explicit calculations using the operator-product expansion, suggest that the
gluon mass falls off as the inverse square of the momentum, relating it to the
gauge-invariant gluon condensate of dimension four. In this article we
demonstrate that the power-law running of the effective gluon mass is indeed
dynamically realized at the level of the non-perturbative Schwinger-Dyson
equation. We study a gauge-invariant non-linear integral equation involving the
gluon self-energy, and establish the conditions necessary for the existence of
infrared finite solutions, described in terms of a momentum-dependent gluon
mass. Assuming a simplified form for the gluon propagator, we derive a
secondary integral equation that controls the running of the mass in the deep
ultraviolet. Depending on the values chosen for certain parameters entering
into the Ansatz for the fully-dressed three-gluon vertex, this latter equation
yields either logarithmic solutions, familiar from previous linear studies, or
a new type of solutions, displaying power-law running. In addition, it
furnishes a non-trivial integral constraint, which restricts significantly (but
does not determine fully) the running of the mass in the intermediate and
infrared regimes. The numerical analysis presented is in complete agreement
with the analytic results obtained, showing clearly the appearance of the two
types of momentum-dependence, well-separated in the relevant space of
parameters. Open issues and future directions are briefly discussed.Comment: 37 pages, 5 figure
Dynamical Behaviour of Low Autocorrelation Models
We have investigated the nature of the dynamical behaviour in low
autocorrelation binary sequences. These models do have a glass transition
of a purely dynamical nature. Above the glass transition the dynamics is not
fully ergodic and relaxation times diverge like a power law with close to . Approaching the glass transition
the relaxation slows down in agreement with the first order nature of the
dynamical transition. Below the glass transition the system exhibits aging
phenomena like in disordered spin glasses. We propose the aging phenomena as a
precise method to determine the glass transition and its first order nature.Comment: 19 pages + 14 figures, LateX, figures uuencoded at the end of the
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