5,370 research outputs found
A rejection-free Monte Carlo method for the hard-disk system
We construct a rejection-free Monte Carlo method for the hard-disk system.
Rejection-free Monte Carlo methods preserve the time-evolution behavior of the
standard Monte Carlo method, and this relationship is confirmed for our method
by observing nonequilibrium relaxation of a bond-orientational order parameter.
The rejection-free method gives a greater computational efficiency than the
standard method at high densities. The rejection free method is implemented in
a shrewd manner using optimization methods to calculate a rejection probability
and to update the system. This method should allow an efficient study of the
dynamics of two-dimensional solids at high density.Comment: 8 pages, 9 figures. This paper has been combined into the
cond-mat/0508652, and published in Phys. Rev.
Model for reflection and transmission matrices of nanowire end facets
Nanowires show a large potential for various electrooptical devices, such as
light emitting diodes, solar cells and nanowire lasers. We present a direct
method developed to calculate the modal reflection and transmission matrix at
the end facets of a waveguide of arbitrary cross section, resulting in a
generalized version of the Fresnel equations. The reflection can be
conveniently computed using Fast Fourier Transforms. We demonstrate that the
reflection is qualitatively described by two main parameters, the modal field
confinement and the average Fresnel reflection of the plane waves constituting
the waveguide mode.Comment: 11 pages,14 figure
Quantum Decoherence at Finite Temperatures
We study measures of decoherence and thermalization of a quantum system
in the presence of a quantum environment (bath) . The whole system is
prepared in a canonical thermal state at a finite temperature. Applying
perturbation theory with respect to the system-environment coupling strength,
we find that under common Hamiltonian symmetries, up to first order in the
coupling strength it is sufficient to consider the uncoupled system to predict
decoherence and thermalization measures of . This decoupling allows closed
form expressions for perturbative expansions for the measures of decoherence
and thermalization in terms of the free energies of and of . Numerical
results for both coupled and decoupled systems with up to 40 quantum spins
validate these findings.Comment: 5 pages, 3 figure
Backaction in metasurface etalons
We consider the response of etalons created by a combination of a
conventional mirror and a metasurface, composed of a periodic lattice of metal
scatterers with a resonant response. This geometry has been used previously for
perfect absorption, in so-called Salisbury screens, and for hybridization of
localized plasmons with Fabry-Perot resonances. The particular aspect we
address is if one can assume an environment-independent reflectivity for the
metasurface when calculating the reflectivity of the composite system, as in a
standard Fabry-Perot analysis, or whether the fact that the metasurface
interacts with its own mirror image renormalizes its response. Using lattice
sum theory, we take into account all possible retarded dipole-dipole
interactions of scatterers in the metasurface amongst each other, and through
the mirror. We show that while a layer-by-layer Fabry-Perot formalism captures
the main qualitative features of metasurface etalons, in fact the mirror
modifies both the polarizability and reflectivity of the metasurface in a
fashion that is akin to Drexhage's modification of the radiative properties of
a single dipole.Comment: 10 pages, 5 figure
Renormalization and additional degrees of freedom within the chiral effective theory for spin-1 resonances
We study in detail various aspects of the renormalization of the spin-1
resonance propagator in the effective field theory framework. First, we briefly
review the formalisms for the description of spin-1 resonances in the path
integral formulation with the stress on the issue of propagating degrees of
freedom. Then we calculate the one-loop 1-- meson self-energy within the
Resonance chiral theory in the chiral limit using different methods for the
description of spin-one particles, namely the Proca field, antisymmetric tensor
field and the first order formalisms. We discuss in detail technical aspects of
the renormalization procedure which are inherent to the power-counting
non-renormalizable theory and give a formal prescription for the organization
of both the counterterms and one-particle irreducible graphs. We also construct
the corresponding propagators and investigate their properties. We show that
the additional poles corresponding to the additional one-particle states are
generated by loop corrections, some of which are negative norm ghosts or
tachyons. We count the number of such additional poles and briefly discuss
their physical meaning.Comment: 65 pages, 12 figure
A projection method for statics and dynamics of lattice spin systems
A method based on Monte Carlo sampling of the probability flows projected
onto the subspace of one or more slow variables is proposed for investigation
of dynamic and static properties of lattice spin systems. We illustrate the
method by applying it, with projection onto the order-parameter subspace, to
the three-dimensional 3-state Potts model in equilibrium and to metastable
decay in a three-dimensional 3-state kinetic Potts model.Comment: 4 pages, 3 figures, RevTex, final version to appear in Phys. Rev.
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Dispersive construction of two-loop P->3\pi (P=K,\eta) amplitudes
The branching ratio of the \eta->3\pi decay is an important source of
information on the value of the quark mass ratio 1/R=(m_d-m_u)/(m_s-\hat m).
Furthermore, isospin breaking effects in the decays K->3\pi provide information
on the pion scattering lengths. The cusp effect in the K->3\pi decays is
presently being analyzed by the NA48 and KTeV experiments. From the theoretical
point of view, these processes have been studied by different methods. We
propose a unified and relativistic treatment relying on very general
principles, unitarity, analyticity and crossing symmetry, combined with chiral
counting, in order to construct model-independent representations of the
corresponding amplitudes that are valid at two loops. A general description of
the procedure is given and is illustrated in the case of the \eta decay
amplitude in the leading order in the isospin breaking.Comment: Talk given at "International Workshop on Effective Field Theories:
from the pion to the upsilon", February 2009, Valencia, Spain. 8 pages. PoS
styl
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