3,973 research outputs found
Universal ratios along a line of critical points. The Ashkin--Teller model
The two-dimensional Ashkin-Teller model provides the simplest example of a
statistical system exhibiting a line of critical points along which the
critical exponents vary continously. The scaling limit of both the paramagnetic
and ferromagnetic phases separated by the critical line are described by the
sine-Gordon quantum field theory in a given range of its dimensionless
coupling. After computing the relevant matrix elements of the order and
disorder operators in this integrable field theory, we determine the universal
amplitude ratios along the critical line within the two-particle approximation
in the form factor approach.Comment: 31 pages, late
Single-photon signals at LEP in supersymmetric models with a light gravitino
We study the single-photon signals expected at LEP in models with a very
light gravitino. The dominant process is neutralino-gravitino production (e+e-
-> chi+ G) with subsequent neutralino decay via chi->gamma+G, giving a
gamma+E_miss signal. We first calculate the cross section at arbitrary
center-of-mass energies and provide new analytic expressions for the
differential cross section valid for general neutralino compositions. We then
consider the constraints on the gravitino mass from LEP 1 and LEP161
single-photon searches, and possible such searches at the Tevatron. We show
that it is possible to evade the stringent LEP 1 limits and still obtain an
observable rate at LEP 2, in particular in the region of parameter space that
may explain the CDF e+e+gamma+gamma+E_T,miss event. As diphoton events from
neutralino pair-production would not be kinematically accessible in this
scenario, the observation of whichever photonic signal will discriminate among
the various light-gravitino scenarios in the literature. We also perform a
Monte Carlo simulation of the expected energy and angular distributions of the
emitted photon, and of the missing invariant mass expected in the events.
Finally we specialize the results to the case of a recently proposed
one-parameter no-scale supergravity model.Comment: 31 pages, LaTeX, 14 figures (included
Constructing a uniform plane-filling path in the ternary heptagrid of the hyperbolic plane
In this paper, we distinguish two levels for the plane-filling property. We
consider a simple and a strong one. In this paper, we give the construction
which proves that the simple plane-filling property also holds for the
hyperbolic plane. The plane-filling property was established for the Euclidean
plane by J. Kari, in 1994, in the strong version
Scaling and Crossover in the Large-N Model for Growth Kinetics
The dependence of the scaling properties of the structure factor on space
dimensionality, range of interaction, initial and final conditions, presence or
absence of a conservation law is analysed in the framework of the large-N model
for growth kinetics. The variety of asymptotic behaviours is quite rich,
including standard scaling, multiscaling and a mixture of the two. The
different scaling properties obtained as the parameters are varied are
controlled by a structure of fixed points with their domains of attraction.
Crossovers arising from the competition between distinct fixed points are
explicitely obtained. Temperature fluctuations below the critical temperature
are not found to be irrelevant when the order parameter is conserved. The model
is solved by integration of the equation of motion for the structure factor and
by a renormalization group approach.Comment: 48 pages with 6 figures available upon request, plain LaTe
Fate of the classical false vacuum
Thermalisation of configurations with initial white noise power spectrum is
studied in numerical simulations of a classical one-component theory
in 2+1 dimensions, coupled to a small amplitude homogenous external field. The
study is performed for energy densities corresponding to the broken symmetry
phase of the system in equilibrium. The effective equation of the order
parameter motion is reconstructed from its trajectory which starts from an
initial value near the metastable point and ends in the stable ground state.
This phenomenological theory quantitatively accounts for the decay of the false
vacuum. The large amplitude transition of the order parameter between the two
minima displays characteristics reflecting dynamical aspects of the Maxwell
construction.Comment: RevTeX 16 pages, 10 Postscript figures, version accepted in Phys.
Rev.
Temporally disordered Ising models
We present a study of the influence of different types of disorder on systems
in the Ising universality class by employing both a dynamical field theory
approach and extensive Monte Carlo simulations. We reproduce some well known
results for the case of quenched disorder (random temperature and random
field), and analyze the effect of four different types of time-dependent
disorder scarcely studied so far in the literature. Some of them are of obvious
experimental and theoretical relevance (as for example, globally fluctuating
temperatures or random fields). All the predictions coming from our field
theoretical analysis are fully confirmed by extensive simulations in two and
three dimensions, and novel qualitatively different, non-Ising transitions are
reported. Possible experimental setups designed to explore the described
phenomenologies are also briefly discussed.Comment: Submitted to Phys. Rev. E. Rapid Comm. 4 page
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