8,660 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
An Extension of the Invariance Principle for a Class of Differential Equations with Finite Delay
An extension of the uniform invariance principle for ordinary differential equations with finite delay is developed. The uniform invariance principle allows the derivative of the auxiliary scalar function V to be positive in some bounded sets of the state space while the classical invariance principle assumes that. V <= 0. As a consequence, the uniform invariance principle can deal with a larger class of problems. The main difficulty to prove an invariance principle for functional differential equations is the fact that flows are defined on an infinite dimensional space and, in such spaces, bounded solutions may not be precompact. This difficulty is overcome by imposing the vector field taking bounded sets into bounded sets
What if the Masses of the First Two Quark Families are not Generated by the Standard Higgs?
We point out that, in the context of the SM, is
expected to be large, of order one. The fact that motivates the introduction of a symmetry S which
leads to , with only the third generation of
quarks acquiring mass. We consider two scenarios for generating the mass of the
first two quark generations and full quark mixing. One consists of the
introduction of a second Higgs doublet which is neutral under S. The second
scenario consists of assuming New Physics at a high energy scale , contributing
to the masses of light quark generations, in an effective field theory
approach. This last scenario leads to couplings of the Higgs particle to
and which are significantly enhanced with
respect to those of the SM. In both schemes, one has scalar-mediated flavour-
changing neutral currents which are naturally suppressed. Flavour violating top
decays are predicted in the second scenario at the level \mbox{Br} (t
\rightarrow h c ) \geq 5\times 10^{-5}.Comment: 11 pages, 1 figur
Strong superadditivity and monogamy of the Renyi measure of entanglement
Employing the quantum R\'enyi -entropies as a measure of
entanglement, we numerically find the violation of the strong superadditivity
inequality for a system composed of four qubits and . This violation
gets smaller as and vanishes for when the
measure corresponds to the Entanglement of Formation (EoF). We show that the
R\'enyi measure aways satisfies the standard monogamy of entanglement for
, and only violates a high order monogamy inequality, in the rare
cases in which the strong superadditivity is also violated. The sates
numerically found where the violation occurs have special symmetries where both
inequalities are equivalent. We also show that every measure satisfing monogamy
for high dimensional systems also satisfies the strong superadditivity
inequality. For the case of R\'enyi measure, we provide strong numerical
evidences that these two properties are equivalent.Comment: replaced with final published versio
Entanglement Irreversibility From Quantum Discord And Quantum Deficit.
We relate the problem of irreversibility of entanglement with the recently defined measures of quantum correlation--quantum discord and one-way quantum deficit. We show that the entanglement of formation is always strictly larger than the coherent information and the entanglement cost is also larger in most cases. We prove irreversibility of entanglement under local operations and classical communication for a family of entangled states. This family is a generalization of the maximally correlated states for which we also give an analytic expression for the distillable entanglement, the relative entropy of entanglement, the distillable secret key, and the quantum discord.10702050
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