176 research outputs found
Decoupling the coupled DGLAP evolution equations: an analytic solution to pQCD
Using Laplace transform techniques, along with newly-developed accurate
numerical inverse Laplace transform algorithms, we decouple the solutions for
the singlet structure function and of the two
leading-order coupled singlet DGLAP equations, allowing us to write fully
decoupled solutions: F_s(x,Q^2)={\cal F}_s(F_{s0}(x), G_0(x)), G(x,Q^2)={\cal
G}(F_{s0}(x), G_0(x)). Here and are known
functions---found using the DGLAP splitting functions---of the functions
and , the chosen
starting functions at the virtuality . As a proof of method, we compare
our numerical results from the above equations with the published MSTW LO gluon
and singlet distributions, starting from their initial values at . Our method completely decouples the two LO distributions, at the same
time guaranteeing that both distributions satisfy the singlet coupled DGLAP
equations. It furnishes us with a new tool for readily obtaining the effects of
the starting functions (independently) on the gluon and singlet structure
functions, as functions of both and . In addition, it can also be
used for non-singlet distributions, thus allowing one to solve analytically for
individual quark and gluon distributions values at a given and , with
typical numerical accuracies of about 1 part in , rather than having to
evolve numerically coupled integral-differential equations on a two-dimensional
grid in , as is currently done.Comment: 6 pages, 2 figure
A new numerical method for obtaining gluon distribution functions , from the proton structure function
An exact expression for the leading-order (LO) gluon distribution function
from the DGLAP evolution equation for the proton structure
function for deep inelastic scattering has
recently been obtained [M. M. Block, L. Durand and D. W. McKay, Phys. Rev.
D{\bf 79}, 014031, (2009)] for massless quarks, using Laplace transformation
techniques. Here, we develop a fast and accurate numerical inverse Laplace
transformation algorithm, required to invert the Laplace transforms needed to
evaluate , and compare it to the exact solution. We obtain accuracies
of less than 1 part in 1000 over the entire and spectrum. Since no
analytic Laplace inversion is possible for next-to-leading order (NLO) and
higher orders, this numerical algorithm will enable one to obtain accurate NLO
(and NNLO) gluon distributions, using only experimental measurements of
.Comment: 9 pages, 2 figure
Numerical Solutions of Matrix Differential Models using Cubic Matrix Splines II
This paper presents the non-linear generalization of a previous work on
matrix differential models. It focusses on the construction of approximate
solutions of first-order matrix differential equations Y'(x)=f(x,Y(x)) using
matrix-cubic splines. An estimation of the approximation error, an algorithm
for its implementation and illustrative examples for Sylvester and Riccati
matrix differential equations are given.Comment: 14 pages; submitted to Math. Comp. Modellin
Helicity Analysis of Semileptonic Hyperon Decays Including Lepton Mass Effects
Using the helicity method we derive complete formulas for the joint angular
decay distributions occurring in semileptonic hyperon decays including lepton
mass and polarization effects. Compared to the traditional covariant
calculation the helicity method allows one to organize the calculation of the
angular decay distributions in a very compact and efficient way. In the
helicity method the angular analysis is of cascade type, i.e. each decay in the
decay chain is analyzed in the respective rest system of that particle. Such an
approach is ideally suited as input for a Monte Carlo event generation program.
As a specific example we take the decay () followed by the nonleptonic decay for which we show a few examples of decay distributions which are
generated from a Monte Carlo program based on the formulas presented in this
paper. All the results of this paper are also applicable to the semileptonic
and nonleptonic decays of ground state charm and bottom baryons, and to the
decays of the top quark.Comment: Published version. 40 pages, 11 figures included in the text. Typos
corrected, comments added, references added and update
corrections to the polar angle dependence of the longitudinal spin-spin correlation asymmetry in
We provide analytical results for the corrections to the polar
angle dependence of the longitudinal spin-spin correlation asymmetry in
. For top quark pair production the
corrections to the longitudinal spin-spin asymmetry are strongly polar angle
dependent and can amount up to in the -range from above
threshold up to GeV. The radiative corrections
to the correlation asymmetry are below in the forward direction where the
cross section is largest. In the case the
corrections reduce the asymmetry value from its value of to
approximately for -values around the peak and are practically
independent of the value of the polar angle theta. This reduction can be traced
to finite anomalous contributions from residual mass effects which survive the
limit. We discuss the role of the anomalous contributions and the
pattern of how they contribute to spin-flip and non-flip terms.Comment: 32 pages written in LaTeX, including 8 encapsulated postscript
figures and 2 tables; v2: corrections according to the erratu
Measurement of the photon-jet production differential cross section in collisions at \sqrt{s}=1.96~\TeV
We present measurements of the differential cross section dsigma/dpT_gamma
for the inclusive production of a photon in association with a b-quark jet for
photons with rapidities |y_gamma|< 1.0 and 30<pT_gamma <300 GeV, as well as for
photons with 1.5<|y_gamma|< 2.5 and 30< pT_gamma <200 GeV, where pT_gamma is
the photon transverse momentum. The b-quark jets are required to have pT>15 GeV
and rapidity |y_jet| < 1.5. The results are based on data corresponding to an
integrated luminosity of 8.7 fb^-1, recorded with the D0 detector at the
Fermilab Tevatron Collider at sqrt(s)=1.96 TeV. The measured cross
sections are compared with next-to-leading order perturbative QCD calculations
using different sets of parton distribution functions as well as to predictions
based on the kT-factorization QCD approach, and those from the Sherpa and
Pythia Monte Carlo event generators.Comment: 10 pages, 9 figures, submitted to Phys. Lett.
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Electrodeposition of Co-Ni-MoxOy Powders: Part I. The Influence of Deposition Conditions on Powder Composition and Morphology
The Co-Ni-MoxOy powders were obtained electrochemically at a constant current density from ammonia electrolyte. Ni and Co were anomalously deposited, inducing Mo deposition, which cannot be deposited separately from aqueous solutions. The obtained Co-Ni-MoxOy powders were investigated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and scanning electon microscope (SEM) methods. Based on the obtained experimental results, it was concluded that the particle size of deposited powders is influenced by the chemical composition of the electrolyte and current density imposed. XRD results suggested that obtained powders were of amorphous structure, although a Co3Mo compound can be formed if certain experimental conditions are applied
Identification of common genetic risk variants for autism spectrum disorder
Autism spectrum disorder (ASD) is a highly heritable and heterogeneous group of neurodevelopmental phenotypes diagnosed in more than 1% of children. Common genetic variants contribute substantially to ASD susceptibility, but to date no individual variants have been robustly associated with ASD. With a marked sample-size increase from a unique Danish population resource, we report a genome-wide association meta-analysis of 18,381 individuals with ASD and 27,969 controls that identified five genome-wide-significant loci. Leveraging GWAS results from three phenotypes with significantly overlapping genetic architectures (schizophrenia, major depression, and educational attainment), we identified seven additional loci shared with other traits at equally strict significance levels. Dissecting the polygenic architecture, we found both quantitative and qualitative polygenic heterogeneity across ASD subtypes. These results highlight biological insights, particularly relating to neuronal function and corticogenesis, and establish that GWAS performed at scale will be much more productive in the near term in ASD.Peer reviewe
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