3,436 research outputs found
Comparison of numerical solutions for Q^2 evolution equations
Q^2 evolution equations are important not only for describing hadron
reactions in accelerator experiments but also for investigating
ultrahigh-energy cosmic rays. The standard ones are called DGLAP evolution
equations, which are integrodifferential equations. There are methods for
solving the Q^2 evolution equations for parton-distribution and fragmentation
functions. Because the equations cannot be solved analytically, various methods
have been developed for the numerical solution. We compare brute-force,
Laguerre-polynomial, and Mellin-transformation methods particularly by focusing
on the numerical accuracy and computational efficiency. An efficient solution
could be used, for example, in the studies of a top-down scenario for the
ultrahigh-energy cosmic rays.Comment: 12 pages, LaTeX, 13 eps files, Journal of Computational Physics in
press, http://hs.phys.saga-u.ac.j
Two-integral distribution functions for axisymmetric stellar systems with separable densities
We show different expressions of distribution functions (DFs) which depend
only on the two classical integrals of the energy and the magnitude of the
angular momentum with respect to the axis of symmetry for stellar systems with
known axisymmetric densities. The density of the system is required to be a
product of functions separable in the potential and the radial coordinate,
where the functions of the radial coordinate are powers of a sum of a square of
the radial coordinate and its unit scale. The even part of the two-integral DF
corresponding to this type of density is in turn a sum or an infinite series of
products of functions of the energy and of the magnitude of the angular
momentum about the axis of symmetry. A similar expression of its odd part can
be also obtained under the assumption of the rotation laws. It can be further
shown that these expressions are in fact equivalent to those obtained by using
Hunter and Qian's contour integral formulae for the system. This method is
generally computationally preferable to the contour integral method. Two
examples are given to obtain the even and odd parts of their two-integral DFs.
One is for the prolate Jaffe model and the other for the prolate Plummer model.
It can be also found that the Hunter-Qian contour integral formulae of the
two-integral even DF for axisymmetric systems can be recovered by use of the
Laplace-Mellin integral transformation originally developed by Dejonghe.Comment: 1 figur
The Mellin Transform Technique for the Extraction of the Gluon Density
A new method is presented to determine the gluon density in the proton from
jet production in deeply inelastic scattering. By using the technique of Mellin
transforms not only for the solution of the scale evolution equation of the
parton densities but also for the evaluation of scattering cross sections, the
gluon density can be extracted in next-to-leading order QCD. The method
described in this paper is, however, more general, and can be used in
situations where a repeated fast numerical evaluation of scattering cross
sections for varying parton distribution functions is required.Comment: 13 pages (LaTeX); 2 figures are included via epsfig; the
corresponding postscript files are uuencode
Improved Fourier Mellin Invariant for Robust Rotation Estimation with Omni-cameras
Spectral methods such as the improved Fourier Mellin Invariant (iFMI)
transform have proved faster, more robust and accurate than feature based
methods on image registration. However, iFMI is restricted to work only when
the camera moves in 2D space and has not been applied on omni-cameras images so
far. In this work, we extend the iFMI method and apply a motion model to
estimate an omni-camera's pose when it moves in 3D space. This is particularly
useful in field robotics applications to get a rapid and comprehensive view of
unstructured environments, and to estimate robustly the robot pose. In the
experiment section, we compared the extended iFMI method against ORB and AKAZE
feature based approaches on three datasets showing different type of
environments: office, lawn and urban scenery (MPI-omni dataset). The results
show that our method boosts the accuracy of the robot pose estimation two to
four times with respect to the feature registration techniques, while offering
lower processing times. Furthermore, the iFMI approach presents the best
performance against motion blur typically present in mobile robotics.Comment: 5 pages, 4 figures, 1 tabl
Towards a global analysis of polarized parton distributions
We present a technique for implementing in a fast way, and without any
approximations, higher-order calculations of partonic cross sections into
global analyses of parton distribution functions. The approach, which is set up
in Mellin-moment space, is particularly suited for analyses of future data from
polarized proton-proton collisions, but not limited to this case. The
usefulness and practicability of this method is demonstrated for the
semi-inclusive production of hadrons in deep-inelastic scattering and the
transverse momentum distribution of ``prompt'' photons in pp collisions, and a
case study for a future global analysis of polarized parton densities is
presented.Comment: 20 pages, LaTeX, 6 eps figures, final version to appear in PRD (minor
changes
A Mellin Space Program for W^{+/-} and Z^0 Production at NNLO
We present a program for the evaluation of full unpolarized cross sections
for the W^{+/-} and Z^0 production in the narrow width approximation at NNLO in
perturbative QCD using Mellin space techniques.Comment: 4 pages, 1 figure. Proceedings of the 10th Hellenic School on
Elementary Particle Physics and Gravity, Corfu 2010, to be published in
Fortschritte der Physi
New prospects for the numerical calculation of Mellin-Barnes integrals in Minkowskian kinematics
During the last several years remarkable progress has been made in numerical
calculations of dimensionally regulated multi-loop Feynman diagrams using
Mellin-Barnes (MB) representations. The bottlenecks were non-planar diagrams
and Minkowskian kinematics. The method has been proved to work in highly
non-trivial physical application (two-loop electroweak bosonic corrections to
the decay), and cross-checked with the sector decomposition
(SD) approach. In fact, both approaches have their pros and cons. In
calculation of multidimensional integrals, depending on masses and scales
involved, they are complementary. A powerful top-bottom approach to the
numerical integration of multidimensional MB integrals is automatized in the
MB-suite AMBRE/MB/ MBtools/MBnumerics/CUBA. Key elements are a dedicated use of
the Cheng-Wu theorem for non-planar topologies and of shifts and deformations
of the integration contours. An alternative bottom-up approach starting with
complex 1-dimensional MB-integrals, based on the exploration of steepest
descent integration contours in Minkowskian kinematics, is also discussed.
Short and long term prospects of the MB-method for multi-loop applications to
LHC- and LC-physics are discussed.Comment: Presented at the Epiphany Cracow conference 2017, refs adde
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