326 research outputs found
Transmission Resonance in an Infinite Strip of Phason-Defects of a Penrose Approximant Network
An exact method that analytically provides transfer matrices in finite
networks of quasicrystalline approximants of any dimensionality is discussed.
We use these matrices in two ways: a) to exactly determine the band structure
of an infinite approximant network in analytical form; b) to determine, also
analytically, the quantum resistance of a finite strip of a network under
appropriate boundary conditions. As a result of a subtle interplay between
topology and phase interferences, we find that a strip of phason-defects along
a special symmetry direction of a low 2-d Penrose approximant, leads to the
rigorous vanishing of the reflection coefficient for certain energies. A
similar behavior appears in a low 3-d approximant. This type of ``resonance" is
discussed in connection with the gap structure of the corresponding ordered
(undefected) system.Comment: 18 pages special macros jnl.tex,reforder.tex, eqnorder.te
Spherical Hartree-Fock calculations with linear momentum projection before the variation.Part I: Energies, form factors, charge densities and mathematical sum rules
Spherical Hartree--Fock calculations with projection onto zero total linear
momentum before the variation are performed for the nuclei 4He, 12C, 16O, 28Si,
32S and 40Ca using a density--independent effective nucleon--nucleon
interaction. The results are compared to those of usual spherical Hartree--Fock
calculations subtracting the kinetic energy of the center of mass motion either
before or after the variation and to the results obtained analytically with
oscillator occupations. Total energies, hole--energies, elastic charge form
factors and charge densities and the mathematical Coulomb sum rules are
discussed.Comment: 16 pages, 13 postscript figure
A geometrical origin for the covariant entropy bound
Causal diamond-shaped subsets of space-time are naturally associated with
operator algebras in quantum field theory, and they are also related to the
Bousso covariant entropy bound. In this work we argue that the net of these
causal sets to which are assigned the local operator algebras of quantum
theories should be taken to be non orthomodular if there is some lowest scale
for the description of space-time as a manifold. This geometry can be related
to a reduction in the degrees of freedom of the holographic type under certain
natural conditions for the local algebras. A non orthomodular net of causal
sets that implements the cutoff in a covariant manner is constructed. It gives
an explanation, in a simple example, of the non positive expansion condition
for light-sheet selection in the covariant entropy bound. It also suggests a
different covariant formulation of entropy bound.Comment: 20 pages, 8 figures, final versio
Numerical loop quantum cosmology: an overview
A brief review of various numerical techniques used in loop quantum cosmology
and results is presented. These include the way extensive numerical simulations
shed insights on the resolution of classical singularities, resulting in the
key prediction of the bounce at the Planck scale in different models, and the
numerical methods used to analyze the properties of the quantum difference
operator and the von Neumann stability issues. Using the quantization of a
massless scalar field in an isotropic spacetime as a template, an attempt is
made to highlight the complementarity of different methods to gain
understanding of the new physics emerging from the quantum theory. Open
directions which need to be explored with more refined numerical methods are
discussed.Comment: 33 Pages, 4 figures. Invited contribution to appear in Classical and
Quantum Gravity special issue on Non-Astrophysical Numerical Relativit
Customer Specific Transaction Risk Management in eCommerce
Increasing potential for turnover in e-commerce is inextricably linked with an increase in risk. Online retailers (e-tailers), aiming for a company-wide value orientation should manage this risk. However, current approaches to risk management either use average retail prices elevated by an overall risk premium or restrict the payment methods offered to customers. Thus, they neglect customer-specific value and risk attributes and leave turnover potentials unconsidered. To close this gap, an innovative valuation model is proposed in this contribution that integrates customer-specific risk and potential turnover. The approach presented evaluates different payment methods using their risk-turnover characteristic, provides a risk-adjusted decision basis for selecting payment methods and allows e-tailers to derive automated risk management decisions per customer and transaction without reducing turnover potential
Studying Gaugino Mass Unification at the LHC
We begin a systematic study of how gaugino mass unification can be probed at
the CERN Large Hadron Collider (LHC) in a quasi-model independent manner. As a
first step in that direction we focus our attention on the theoretically
well-motivated mirage pattern of gaugino masses, a one-parameter family of
models of which universal (high scale) gaugino masses are a limiting case. We
improve on previous methods to define an analytic expression for the metric on
signature space and use it to study one-parameter deviations from universality
in the gaugino sector, randomizing over other soft supersymmetry-breaking
parameters. We put forward three ensembles of observables targeted at the
physics of the gaugino sector, allowing for a determination of this
non-universality parameter without reconstructing individual mass eigenvalues
or the soft supersymmetry-breaking gaugino masses themselves. In this
controlled environment we find that approximately 80% of the supersymmetric
parameter space would give rise to a model for which our method will detect
non-universality in the gaugino mass sector at the 10% level with an integrated
luminosity of order 10 inverse femptobarns. We discuss strategies for improving
the method and for adding more realism in dealing with the actual experimental
circumstances of the LHC
Resolved Photon Processes
We review the present level of knowledge of the hadronic structure of the
photon, as revealed in interactions involving quarks and gluons ``in" the
photon. The concept of photon structure functions is introduced in the
description of deep--inelastic scattering, and existing
parametrizations of the parton densities in the photon are reviewed. We then
turn to hard \gamp\ and \gaga\ collisions, where we treat the production of
jets, heavy quarks, hard (direct) photons, \jpsi\ mesons, and lepton pairs. We
also comment on issues that go beyond perturbation theory, including recent
attempts at a comprehensive description of both hard and soft \gamp\ and \gaga\
interactions. We conclude with a list of open problems.Comment: LaTeX with equation.sty, 85 pages, 29 figures (not included). A
complete PS file of the paper, including figures, can be obtained via
anonymous ftp from
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-898.ps.
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