874 research outputs found
A review of system dynamics models applied in transportation
It is 20 years since Abbas and Bell [1994. “System Dynamics Applicability to Transportation Modeling.” Transportation Research Part A 28 (5): 373–390] evaluated the strengths and weaknesses of system dynamics (SD) as an approach for modelling in the transportation area. They listed 12 advantages of the approach and in particular suggested it was well suited to strategic issues and that it could provide a useful tool for supporting policy analysis and decision-making in the transport field. This paper sets out a review of over 50 peer-reviewed journal papers since 1994 categorising them by area of application and providing a summary of particular insights raised. The fields of application include the take-up of alternate fuel vehicles, supply chain management affecting transport, highway maintenance, strategic policy, airport infrastructure and airline business cycles and a set of emerging application areas. The paper concludes with recommendations for future application of the SD approach
All-order results for soft and collinear gluons
I briefly review some general features and some recent developments
concerning the resummation of long-distance singularities in QCD and in more
general non-abelian gauge theories. I emphasize the field-theoretical tools of
the trade, and focus mostly on the exponentiation of infrared and collinear
divergences in amplitudes, which underlies the resummation of large logarithms
in the corresponding cross sections. I then describe some recent results
concerning the conformal limit, notably the case of N = 4 superymmetric
Yang-Mills theoryComment: 15 pages, invited talk presented at the 10th Workshop in High Energy
Physics Phenomenology (WHEPP X), Chennai, India, January 200
Power Corrections in QCD: A Matter of Energy Resolution
We consider power-like corrections in QCD which can be viewed as power
surpressed infrared singularities. We argue that the presence of these
singularities depends crucially on the energy resolution. In case of poor
energy resolution, i.e., inclusive cross sections, there are constraints on
infrared singularities expressed by the Kinoshita-Lee-Nauenberg (KLN) theorem.
We rewrite the theorem in covariant notations and argue that the KLN theorem
implies the extension of the Bloch-Nordsieck cancellation of logarithmic
singularities to the case of linear corrections.Comment: 11 pages, Latex file, uses epsf.sty, 5 figures in a uufil
Consistent Analysis of the Transition Form Factor in the Whole Physical Region
In the paper, we show that the transition form factor can be
calculated by using the different approach in the different regions and
they are consistent with each other in the whole physical region. For the
transition form factor in the large recoil regions, one can apply the
PQCD approach, where the transverse momentum dependence for both the hard
scattering part and the non-perturbative wavefunction, the Sudakov effects and
the threshold effects are included to regulate the endpoint singularity and to
derive a more reliable PQCD result. Pionic twist-3 contributions are carefully
studied with a better endpoint behavior wavefunction for and we find
that its contribution is less than the leading twist contribution. Both the two
wavefunctions and of the B meson can give sizable
contributions to the transition form factor and should be kept for a
better understanding of the B decays. The present obtained PQCD results can
match with both the QCD light-cone sum rule results and the extrapolated
lattice QCD results in the large recoil regions.Comment: 18pages, 6 figure
A Precision Calculation of the Next-to-Leading Order Energy-Energy Correlation Function
The O(alpha_s^2) contribution to the Energy-Energy Correlation function (EEC)
of e+e- -> hadrons is calculated to high precision and the results are shown to
be larger than previously reported. The consistency with the leading logarithm
approximation and the accurate cancellation of infrared singularities exhibited
by the new calculation suggest that it is reliable. We offer evidence that the
source of the disagreement with previous results lies in the regulation of
double singularities.Comment: 6 pages, uuencoded LaTeX and one eps figure appended Complete paper
as PostScript file (125 kB) available at:
http://www.phys.washington.edu/~clay/eecpaper1/paper.htm
Effects of Higher-Order Threshold Corrections in High-E_T Jet Production
Results for higher-order threshold enhancements in high-E_T jet production in
hadron-hadron collisions are presented. Expressions are given for the
next-to-next-to-leading order (NNLO) threshold corrections to the single-jet
inclusive cross section at next-to-leading logarithmic (NLL) accuracy. The
corrections are found to be small for the specific choice of E_T/2 for the
factorization and renormalization scales, and the corrected cross section shows
a substantial reduction of the scale dependence. A comparison to experimental
results from the Tevatron is presented.Comment: 24 pages LaTeX, 5 figure
Jet Algorithms and Top Quark Mass Measurement
Mass measurements of objects that decay into hadronic jets, such as the top
quark, are shown to be improved by using a variant of the jet algorithm
in place of standard cone algorithms. The possibility and importance of better
estimating the neutrino component in tagged jets is demonstrated. These
techniques will also be useful in the search for Higgs boson .Comment: 35 pages, REVTeX, 14 figures (epsf) Final expanded version to appear
in Physical Review
Effects of Parton Intrinsic Transverse Momentum on Photon Production in Hard-Scattering Processes
We calculate the photon production cross section arising from the hard
scattering of partons in nucleon-nucleon collisions by taking into account the
intrinsic parton transverse momentum distribution and the next-to-leading-order
contributions. As first pointed out by Owens, the inclusion of the intrinsic
transverse momentum distribution of partons leads to an enhancement of photon
production cross section in the region of photon transverse momenta of a few
GeV/c for nucleon-nucleon collisions at a center-of-mass energy of a few tens
of GeV. The enhancement increases as decreases. Such an enhancement
is an important consideration in the region of photon momenta under
investigation in high-energy heavy-ion collisions.Comment: 10 pages, 9 figures, in LaTex, revised to include ananlytic
evaluation of the hard-scattering integra
Large distance behaviour of light cone operator product in perturbative and nonperturbative QCD regimes
We evaluate the coordinate space dependence of the matrix elements of the
commutator of the electromagnetic and gluon currents in the vicinity of the
light-cone but at large distances within the parton model, DGLAP, the
resummation approaches to the small x behaviour of DIS processes, and for the
Unitarity Bound. We find that an increase of the commutator with relative
distance as is the generic property of QCD
at small but fixed space-time interval in perturbative and
nonperturbative QCD regimes. We explain that the factor follows within the
dipole model (QCD factorization theorem) from the properties of Lorents
transformation. The increase of disappeares at central impact parameters
if cross section of DIS may achieve the Unitarity Limit. We argue that such
long range forces are hardly consistent with thermodynamic equilibrium while a
Unitarity Limit may signal equilibration. Possible implications of this new
long range interaction are briefly discussed.Comment: 23 page
Joint Resummation for Higgs Production
We study the application of the joint resummation formalism to Higgs
production via gluon-gluon fusion at the LHC, defining inverse transforms by
analytic continuation. We work at next-to-leading logarithmic accuracy. We find
that at low Q_T the resummed Higgs Q_T distributions are comparable in the
joint and pure-Q_T formalisms, with relatively small influence from threshold
enhancement in this range. We find a modest (about ten percent) decrease in the
inclusive cross section, relative to pure threshold resummation.Comment: 22 pages, LaTeX, 5 figures as eps file
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