32,079 research outputs found
Scaling properties of a ferromagnetic thin film model at the depinning transition
In this paper, we perform a detailed study of the scaling properties of a
ferromagnetic thin film model. Recently, interest has increased in the scaling
properties of the magnetic domain wall (MDW) motion in disordered media when an
external driving field is present. We consider a (1+1)-dimensional model, based
on evolution rules, able to describe the MDW avalanches. The global interface
width of this model shows Family-Vicsek scaling with roughness exponent
and growth exponent . In contrast, this
model shows scaling anomalies in the interface local properties characteristic
of other systems with depinning transition of the MDW, e.g. quenched
Edwards-Wilkinson (QEW) equation and random-field Ising model (RFIM) with
driving. We show that, at the depinning transition, the saturated average
velocity vanished very slowly (with ) when the reduced force . The simulation
results show that this model verifies all accepted scaling relations which
relate the global exponents and the correlation length (or time) exponents,
valid in systems with depinning transition. Using the interface tilting method,
we show that the model, close to the depinning transition, exhibits a
nonlinearity similar to the one included in the Kardar-Parisi-Zhang (KPZ)
equation. The nonlinear coefficient with , which implies that as the depinning transition is
approached, a similar qualitatively behaviour to the driven RFIM. We conclude
this work by discussing the main features of the model and the prospects opened
by it.Comment: 10 pages, 5 figures, 1 tabl
Growing interfaces: A brief review on the tilt method
The tilt method applied to models of growing interfaces is a useful tool to
characterize the nonlinearities of their associated equation. Growing
interfaces with average slope , in models and equations belonging to
Kardar-Parisi-Zhang (KPZ) universality class, have average saturation velocity
when .
This property is sufficient to ensure that there is a nonlinearity type square
height-gradient. Usually, the constant is considered equal to the
nonlinear coefficient of the KPZ equation. In this paper, we show
that the mean square height-gradient ,
where for the continuous KPZ equation and otherwise, e.g.
ballistic deposition (BD) and restricted-solid-on-solid (RSOS) models. In order
to find the nonlinear coefficient associated to each system, we
establish the relationship and we test it through the
discrete integration of the KPZ equation. We conclude that height-gradient
fluctuations as function of are constant for continuous KPZ equation and
increasing or decreasing in other systems, such as BD or RSOS models,
respectively.Comment: 11 pages, 4 figure
Scalar Dark Matter in light of LEP and ILC Experiments
In this work we study a scalar field dark matter model with mass of the order
of 100 MeV. We assume dark matter is produced in the process , that, in fact, could be a background for the standard process
extensively studied at LEP. We constrain the
chiral couplings, and , of the dark matter with electrons through an
intermediate fermion of mass GeV and obtain and
for the best fit point of our analysis. We also
analyze the potential of ILC to detect this scalar dark matter for two
configurations: (i) center of mass energy GeV and luminosity
fb, and (ii) center of mass energy TeV
and luminosity fb. The differences of polarized beams
are also explored to better study the chiral couplings.Comment: 15 pages, 6 figures and 1 table. New references added and
improvements in the text. Conclusions unchange
A Hamiltonian functional for the linearized Einstein vacuum field equations
By considering the Einstein vacuum field equations linearized about the
Minkowski metric, the evolution equations for the gauge-invariant quantities
characterizing the gravitational field are written in a Hamiltonian form by
using a conserved functional as Hamiltonian; this Hamiltonian is not the analog
of the energy of the field. A Poisson bracket between functionals of the field,
compatible with the constraints satisfied by the field variables, is obtained.
The generator of spatial translations associated with such bracket is also
obtained.Comment: 5 pages, accepted in J. Phys.: Conf. Serie
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