17,189 research outputs found
Eliminating the Hadronic Uncertainty
The Standard Model Lagrangian requires the values of the fermion masses, the
Higgs mass and three other experimentally well-measured quantities as input in
order to become predictive. These are typically taken to be ,
and . Using the first of these, however, introduces a hadronic
contribution that leads to a significant error. If a quantity could be found
that was measured at high energy with sufficient precision then it could be
used to replace as input. The level of precision required for this to
happen is given for a number of precisely-measured observables. The boson
mass must be measured with an error of \,MeV, to \,MeV
and polarization asymmetry, , to that would seem to be the
most promising candidate. The r\^ole of renormalized parameters in perturbative
calculations is reviewed and the value for the electromagnetic coupling
constant in the renormalization scheme that is consistent
with all experimental data is obtained to be .Comment: 8 pages LaTeX2
Self-consistent field predictions for quenched spherical biocompatible triblock copolymer micelles
We have used the Scheutjens-Fleer self-consistent field (SF-SCF) method to
predict the self-assembly of triblock copolymers with a solvophilic middle
block and sufficiently long solvophobic outer blocks. We model copolymers
consisting of polyethylene oxide (PEO) as solvophilic block and
poly(lactic-co-glycolic) acid (PLGA) or poly({\ko}-caprolactone) (PCL) as
solvophobic block. These copolymers form structurally quenched spherical
micelles provided the solvophilic block is long enough. Predictions are
calibrated on experimental data for micelles composed of PCL-PEO-PCL and
PLGA-PEO-PLGA triblock copolymers prepared via the nanoprecipitation method. We
establish effective interaction parameters that enable us to predict various
micelle properties such as the hydrodynamic size, the aggregation number and
the loading capacity of the micelles for hydrophobic species that are
consistent with experimental finding.Comment: accepted for publication in Soft Matte
Soliton-potential interaction in the nonlinear Klein-Gordon model
The interaction of solitons with external potentials in nonlinear
Klein-Gordon field theory is investigated using an improved model. The
presented model has been constructed with a better approximation for adding the
potential to the Lagrangian through the metric of background space-time. The
results of the model are compared with another model and the differences are
discussed.Comment: 14 pages,8 figure
Kullback--Leibler approximation for probability measures on infinite dimensional spaces
In a variety of applications it is important to extract information from a probability measure on an infinite dimensional space. Examples include the Bayesian approach to inverse problems and (possibly conditioned) continuous time Markov processes. It may then be of interest to find a measure , from within a simple class of measures, which approximates . This problem is studied in the case where the Kullback--Leibler divergence is employed to measure the quality of the approximation. A calculus of variations viewpoint is adopted, and the particular case where is chosen from the set of Gaussian measures is studied in detail. Basic existence and uniqueness theorems are established, together with properties of minimizing sequences. Furthermore, parameterization of the class of Gaussians through the mean and inverse covariance is introduced, the need for regularization is explained, and a regularized minimization is studied in detail. The calculus of variations framework resulting from this work provides the appropriate underpinning for computational algorithms
Kullback--Leibler approximation for probability measures on infinite dimensional spaces
In a variety of applications it is important to extract information from a probability measure on an infinite dimensional space. Examples include the Bayesian approach to inverse problems and (possibly conditioned) continuous time Markov processes. It may then be of interest to find a measure , from within a simple class of measures, which approximates . This problem is studied in the case where the Kullback--Leibler divergence is employed to measure the quality of the approximation. A calculus of variations viewpoint is adopted, and the particular case where is chosen from the set of Gaussian measures is studied in detail. Basic existence and uniqueness theorems are established, together with properties of minimizing sequences. Furthermore, parameterization of the class of Gaussians through the mean and inverse covariance is introduced, the need for regularization is explained, and a regularized minimization is studied in detail. The calculus of variations framework resulting from this work provides the appropriate underpinning for computational algorithms
Measuring the Size of Quasar Broad-Line Clouds Through Time Delay Light-Curve Anomalies of Gravitational Lenses
Intensive monitoring campaigns have recently attempted to measure the time
delays between multiple images of gravitational lenses. Some of the resulting
light-curves show puzzling low-level, rapid variability which is unique to
individual images, superimposed on top of (and concurrent with) longer
time-scale intrinsic quasar variations which repeat in all images. We
demonstrate that both the amplitude and variability time-scale of the rapid
light-curve anomalies, as well as the correlation observed between intrinsic
and microlensed variability, are naturally explained by stellar microlensing of
a smooth accretion disk which is occulted by optically-thick broad-line clouds.
The rapid time-scale is caused by the high velocities of the clouds (~5x10^3
km/s), and the low amplitude results from the large number of clouds covering
the magnified or demagnified parts of the disk. The observed amplitudes of
variations in specific lenses implies that the number of broad-line clouds that
cover ~10% of the quasar sky is ~10^5 per 4 pi steradian. This is comparable to
the expected number of broad line clouds in models where the clouds originate
from bloated stars.Comment: 19 pages, 9 figures. Submitted to Ap
A light-front description of electromagnetic form factors for hadrons
A review of the hadron electromagnetic form factors obtained in a light-front
constituent quark model, based on the eigenfunctions of a mass operator, is
presented. The relevance of different components in the q-q interaction for the
description of hadron experimental form factors is analysed.Comment: 6 pages, Latex, 3 Postscript figures included. Proceedings of
"Nucleon 99", Frascati, June 1999. To appear in Nucl. Phys.
Band gap reduction in GaNSb alloys due to the anion mismatch
The structural and optoelectronic properties in GaNxSb1–x alloys (0<=x<0.02) grown by molecular-beam epitaxy on both GaSb substrates and AlSb buffer layers on GaAs substrates are investigated. High-resolution x-ray diffraction (XRD) and reciprocal space mapping indicate that the GaNxSb1–x epilayers are of high crystalline quality and the alloy composition is found to be independent of substrate, for identical growth conditions. The band gap of the GaNSb alloys is found to decrease with increasing nitrogen content from absorption spectroscopy. Strain-induced band-gap shifts, Moss-Burstein effects, and band renormalization were ruled out by XRD and Hall measurements. The band-gap reduction is solely due to the substitution of dilute amounts of highly electronegative nitrogen for antimony, and is greater than observed in GaNAs with the same N content
On Gauge Invariance of Breit-Wigner Propagators
We present an approach to bosonic () as well as fermionic
(top-quark) Breit-Wigner propagators which is consistent with gauge invariance
arguments. In particular, for the -boson propagator we extend previous
analyses and show that the part proportional to must be
modified near the resonance. We derive a mass shift which agrees with results
obtained elsewhere by different methods. The modified form of a resonant heavy
fermion propagator is also given.Comment: 16 p., TeX, (final version
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