3,444 research outputs found
Kaon semileptonic decay (K_{l3}) form factors from the instanton vacuum
We investigate the kaon semileptonic decay (K_{l3}) form factors within the
framework of the nonlocal chiral quark model from the instanton vacuum, taking
into account the effects of flavor SU(3) symmetry breaking. We also consider
the problem of gauge invariance arising from the momentum-dependent quark mass
in the present work. All theoretical calculations are carried out without any
adjustable parameter, the average instanton size (rho ~ 1/3 fm) and the
inter-instanton distance (R ~ 1 fm) having been fixed. We also show that the
present results satisfy the Callan-Treiman low-energy theorem as well as the
Ademollo-Gatto theorem. Using the K_{l3} form factors, we evaluate relevant
physical quantities. It turns out that the effects of flavor SU(3) symmetry
breaking are essential in reproducing the kaon semileptonic form factors. The
present results are in a good agreement with experiments, and are compatible
with other model calculations.Comment: 12 pages, 3 figures, submitted to PR
511 keV -ray emission from the galactic bulge by MeV millicharged dark matter
We propose a possible explanation for the recently observed anomalous 511 keV
line with a new "millicharged" fermion. This new fermion is light []. Nevertheless, it has never been observed by any collider
experiments by virtue of its tiny electromagnetic charge . In
particular, we constrain parameters of this millicharged particle if the 511
keV cosmic -ray emission from the galactic bulge is due to positron
production from this new particle.Comment: 3 pages, 1 figure, A talk given by J.C.Park at the 16th International
Conference on Supersymmetry and the Unification of Fundamental Interactions
(SUSY08), Seoul, Korea, June 16-21, 200
Mesons and nucleons from holographic QCD in a unified approach
We investigate masses and coupling constants of mesons and nucleons within a
hard wall model of holographic QCD in a unified approach. We first examine an
appropriate form of fermionic solutions by restricting the mass coupling for
the five dimensional bulk fermions and bosons. We then derive approximated
analytic solutions for the nucleons and the corresponding masses in a small
mass coupling region. In order to treat meson and nucleon properties on the
same footing, we introduce the same infrared (IR) cut in such a way that the
meson-nucleon coupling constants, i.e., g_{pi NN} and g_{rho NN} are uniquely
determined. The first order approximation with respect to a dimensionless
expansion parameter, which is valid in the small mass coupling region,
explicitly shows difficulties to avoid the IR scale problem of the hard wall
model. We discuss possible ways of circumventing these problems.Comment: 15 pages, No figure. Several typos have been remove
Machine-Learning-Based Model for Hurricane Storm Surge Forecasting in the Lower Laguna Madre
During every Atlantic hurricane season, storms represent a constant risk to Texan coastal communities and other communities along the Atlantic coast of the United States. A storm surge refers to the abnormal rise of sea water level due to hurricanes and storms; traditionally, hurricane storm surge predictions are generated using complex numerical models that require high amounts of computing power to be run, which grow proportionally with the extent of the area covered by the model. In this work, a machine-learning-based storm surge forecasting model for the Lower Laguna Madre is implemented. The model considers gridded forecasted weather data on winds and atmospheric pressure over the Gulf of Mexico, as well as previous sea levels obtained from a Laguna Madre ocean circulation numerical model. Using architectures such as Convolutional Neural Networks (CNN) and Long Short-Term Memory (LSTM) combined, the resulting model is capable of identifying upcoming hurricanes and predicting storm surges, as well as normal conditions in several locations along the Lower Laguna Madre. Overall, the model is able to predict storm surge peaks with an average difference of 0.04 m when compared with a numerical model and an average RMSE of 0.08 for normal conditions and 0.09 for storm surge conditions
High resolution angle resolved photoemission studies on quasi-particle dynamics in graphite
We obtained the spectral function of the graphite H point using high
resolution angle resolved photoelectron spectroscopy (ARPES). The extracted
width of the spectral function (inverse of the photo-hole lifetime) near the H
point is approximately proportional to the energy as expected from the linearly
increasing density of states (DOS) near the Fermi energy. This is well
accounted by our electron-phonon coupling theory considering the peculiar
electronic DOS near the Fermi level. And we also investigated the temperature
dependence of the peak widths both experimentally and theoretically. The upper
bound for the electron-phonon coupling parameter is ~0.23, nearly the same
value as previously reported at the K point. Our analysis of temperature
dependent ARPES data at K shows that the energy of phonon mode of graphite has
much higher energy scale than 125K which is dominant in electron-phonon
coupling.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
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