54,265 research outputs found
Soft Gluon Approach for Diffractive Photoproduction of J/psi
We study diffractive photoproduction of by taking the charm quark as
a heavy quark. A description of nonperturbative effect related to can
be made by using NRQCD. In the forward region of the kinematics, the
interaction between the -pair and the initial hadron is due to
exchange of soft gluons. The effect of the exchange can be studied by using the
expansion in the inverse of the quark mass . At the leading order we find
that the nonperturbative effect related to the initial hadron is represented by
a matrix element of field strength operators, which are separated in the moving
direction of in the space-time. The S-matrix element is then obtained
without using perturbative QCD and the results are not based on any model.
Corrections to the results can be systematically added. Keeping the dominant
contribution of the S-matrix element in the large energy limit we find that the
imaginary part of the S-matrix element is related to the gluon distribution for
with a reasonable assumption, the real part can be obtained with
another approximation or with dispersion relation. Our approach is different
than previous approaches and also our results are different than those in these
approaches. The differences are discussed in detail. A comparison with
experiment is also made and a qualitative agreement is found.Comment: 25 pages, 6 figures. Tiny changes in two figures, conclusion and text
unchanged, accpeted by Nucl. Phys.
CoCoA: A General Framework for Communication-Efficient Distributed Optimization
The scale of modern datasets necessitates the development of efficient
distributed optimization methods for machine learning. We present a
general-purpose framework for distributed computing environments, CoCoA, that
has an efficient communication scheme and is applicable to a wide variety of
problems in machine learning and signal processing. We extend the framework to
cover general non-strongly-convex regularizers, including L1-regularized
problems like lasso, sparse logistic regression, and elastic net
regularization, and show how earlier work can be derived as a special case. We
provide convergence guarantees for the class of convex regularized loss
minimization objectives, leveraging a novel approach in handling
non-strongly-convex regularizers and non-smooth loss functions. The resulting
framework has markedly improved performance over state-of-the-art methods, as
we illustrate with an extensive set of experiments on real distributed
datasets
An investigation of RAKE receiver operation in an urban environment for various spreading bandwidth allocations
Parton Sum Rules and Improved Scaling Variable
The effect from quark masses and transversal motion on the Gottfried,
Bjorken, and Ellis-Jaffe sum rules is examined by using a quark-parton model of
nucleon structure functions based on an improved scaling variable. Its use
results in corrections to the Gottfried, Bjorken, and Ellis-Jaffe sum rules. We
use the Brodsky-Huang-Lepage prescription of light-cone wavefunctions to
estimate the size of the corrections. We constrain our choice of parameters by
the roughly known higher twist corrections to the Bjorken sum rule and find
that the resulting corrections to the Gottfried and Ellis-Jaffe sum rules are
relevant, though not large enough to explain the observed sum rule violations.Comment: latex, with 1 postscript figure, to be published in Phys.Lett.
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