1,210 research outputs found
One Loop Multiphoton Helicity Amplitudes
We use the solutions to the recursion relations for double-off-shell fermion
currents to compute helicity amplitudes for -photon scattering and
electron-positron annihilation to photons in the massless limit of QED. The
form of these solutions is simple enough to allow {\it all}\ of the
integrations to be performed explicitly. For -photon scattering, we find
that unless , the amplitudes for the helicity configurations (+++...+) and
(-++...+) vanish to one-loop order.Comment: 27 pages + 4 uuencoded figures (included), Fermilab-Pub-93/327-T,
RevTe
Seroprevalence of bluetongue serotype 8 in cattle in the Netherlands in spring 2007, and its consequences
A cross-sectional study was carried out in spring 2007, at the end of the first bluetongue outbreak season, to determine the geographical spread of bluetongue virus serotype 8 (BTV-8) infection in cattle in the Netherlands and the consequences for some production parameters. Blood samples from cattle submitted to the laboratory of the Dutch Animal Health Service for other voluntary and obligatory health programmes were tested serologically for BTV-8. in total, 37,073 samples were tested and 659 (1.78 per cent) were seropositive. The samples came from 5436 herds, of which 45 per cent of herds had only one sample submitted from them. The prevalence was highest in the south of the country, where the outbreak had started, and decreased towards the north. in 340 herds more than 50 per cent of cattle were tested, of which 156 herds were located in infected compartments, and in 37 of these herds (10.9 per cent) at least one positive cow was detected. The average within-herd prevalence in the 37 herds was 39.3 per cent: 2.2 per cent in I I dairy herds, 68.4 per cent in 20 small-scale herds and 14 per cent in four suckler cow herds. The prevalence differed significantly between herd types but did not show a geographical trend. The average net return for milk production amounted to is an element of 2417/cow/year and it decreased significantly on average by is an element of 48/ cow/year in the bluetongue-infected dairy herds during the bluetongue period. on the small-scale farms, the incidence of mortality increased by 3.2 (95 per cent confidence interval [a] 1.2 to 9.1) times in the infected herds during the bluetongue period, but the voluntary culling rate decreased by a factor of 2.3 (95 per cent Cl 1.1 to 4.8)
Time and Organizational Learning: A Review and Agenda for Future Research
This paper examines the time dimensions of organizational learning. While several recent studies have addressed aspects of time in relation to organizational learning, the topic of time has received little attention in reviews of the field, and this promising domain of research is fragmented. The objective of this paper is to bring these dispersed conceptualizations and findings together and to provide a more solid conceptual foundation for the time dimensions of organizational learning as a new research avenue. Three sets of mechanisms are discerned: concerning time as duration; the timing of organizational learning; and the role of the past, present and future in organizational learning. Each of these perspectives offers unique insights, which when integrated can help map new directions for future research
Exact Results on e+ e- --> e+ e- + 2 Photons at SLC/LEP Energies
We use the spinor methods of the CALKUL collaboration, as realized by Xu,
Zhang and Chang, to calculate the differential cross section for e+ e- --> e+
e- + 2 photons for c.m.s. energies in the SLC/LEP regime. An explicit complete
formula for the respective cross section is obtained. The leading log
approximation is used to check the formula. Applications of the formula to high
precision luminosity calculations at SLC/LEP are discussed.Comment: 16 pages(LaTeX), UTHEP-92-0601 (contains corrected figures
Radiative return at e+e- factories
The energy dependence of the electron - positron hadronic cross section can
be measured not only by a straightforward energy scan, but also by means of the
radiative return method. To provide extensive comparisons between theory and
experiment a Monte Carlo event generator is an indispensable tool. We have
developed such a generator called PHOKHARA, which simulates e+e- -> mesons +
photon(s) processes. In this paper we present its latest tests and upgrades.Comment: 5 pages, 7 figures, presented at RADCOR 2002, Kloster Banz, Sept.
8-13, 200
Heavy Top Quark Searches in the Di-Lepton Mode at the Tevatron
We present the results of a detailed study of the effects of -tagging on
the heavy top-quark signal and backgrounds for the modes of the di-lepton plus
two high transverse energy jets at the Fermilab Tevatron. The general
characteristics of the heavy top-quark signal events are also discussed so that
a comparison can be made between -tagging and imposing stringent kinematical
cuts to eliminate backgrounds.Comment: uses PHYZZX and TABLES macros, 10 pages, four figures not included
(available by request), FERMILAB-Pub-93/105-
Numerical evaluation of the general massive 2-loop sunrise self-mass master integrals from differential equations
The system of 4 differential equations in the external invariant satisfied by
the 4 master integrals of the general massive 2-loop sunrise self-mass diagram
is solved by the Runge-Kutta method in the complex plane. The method, whose
features are discussed in details, offers a reliable and robust approach to the
direct and precise numerical evaluation of Feynman graph integrals.Comment: 1+21 pages, Latex, 5 ps-figure
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