608 research outputs found
QCD corrections to e+ e- --> 4 jets
We report on the next-to-leading order QCD calculation for e+ e- --> 4 jets.
We explain some modern techniques which have been used to calculate the
one-loop amplitudes efficiently. We further report on the general purpose
numerical program ``Mercutio'', which can be used to calculate any infrared
safe four-jet quantity in electron-positron annihilation at next-to-leading
order.Comment: 4 pages, talk given at the UK Phenomenology Workshop on Collider
Physics, Durham, 19-24 September 199
QCD Sum Rules for Heavy Flavors
We give a short review of QCD sum rule results for B and D mesons and
Lambda_Q and Sigma_Q baryons. We focus mainly on recent developments concerning
semileptonic B->pion and D->pion transitions, pion couplings to heavy hadrons,
decay constants and estimates of the b quark mass from a baryonic sum rule, and
the extraction of the pion distribution amplitude from CLEO data.Comment: 12 pages, LaTeX, Talk given by O.Yakovlev at the 4th Workshop on
Continuous Advances in QCD, Minneapolis, May 12-14, 2000; to appear in the
Proceeding
Perturbative QCD Correction to the Light-Cone Sum Rule for the and Couplings
The and couplings have previously been derived from a QCD
light-cone sum rule in leading order. Here, we describe the calculation of the
correction to the twist 2 term of this sum rule. The result is
used for a first next-to-leading order analysis. We obtain and , where the error indicates the remaining
theoretical uncertainty.Comment: 11 pages, 1 figure, Latex, epsfi
Generation and analysis of an acoustic radiation pattern database for forty-one musical instruments
A database of acoustic radiation patterns was recorded, modeled, and analyzed for 41 modern or authentic orchestral musical instruments. The generation of this database included recordings of each instrument over the entire chromatic tone range in an anechoic chamber using a surrounding spherical microphone array. Acoustic source centering was applied in order to align the acoustic center of the sound source to the physical center of the microphone array. The acoustic radiation pattern is generated in the spherical harmonics domain at each harmonic partial of each played tone. An analysis of the acoustic radiation pattern complexity has been performed in terms of the number of excitation points using the centering algorithm. The database can be used both for studying the radiation of musical instruments itself, as well as for the implementation of radiation patterns in room acoustical simulations and auralization in order to obtain a spatial excitation of the room closer to reality
On-the-fly memory compression for multibody algorithms.
Memory and bandwidth demands challenge developers of particle-based codes that have to scale on new architectures, as the growth of concurrency outperforms improvements in memory access facilities, as the memory per core tends to stagnate, and as communication networks cannot increase bandwidth arbitrary. We propose to analyse each particle of such a code to find out whether a hierarchical data representation storing data with reduced precision caps the memory demands without exceeding given error bounds. For admissible candidates, we perform this compression and thus reduce the pressure on the memory subsystem, lower the total memory footprint and reduce the data to be exchanged via MPI. Notably, our analysis and transformation changes the data compression dynamically, i.e. the choice of data format follows the solution characteristics, and it does not require us to alter the core simulation code
Feynman graph polynomials
The integrand of any multi-loop integral is characterised after Feynman
parametrisation by two polynomials. In this review we summarise the properties
of these polynomials. Topics covered in this article include among others:
Spanning trees and spanning forests, the all-minors matrix-tree theorem,
recursion relations due to contraction and deletion of edges, Dodgson's
identity and matroids.Comment: 35 pages, references adde
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