2,573 research outputs found
Selected Topics in Top Quark Physics
I discuss three different selected topics in top quark physics. The first
topic concerns the next-to-next-to-leading order calculation of the
hadroproduction of top quark pairs and the role of multiple polylogarithms in
this calculation. I report on an ongoing next-to-next-to-leading order
calculation of heavy quark pair production in hadron collisions where the
loop--by--loop part of the calculation is about to be completed. Calculating
the loop-by-loop part allows one to take a glimpse at the mathematical
structure of the full NNLO calculation. The loop-by-loop contributions bring in
a new class of functions introduced only eight years ago by the Russian
mathematician Goncharov called multiple polylogarithms. The second topic
concerns a next-to-leading order calculation of unpolarized top quark decays
which are analyzed in cascade fashion followed by . Finally, I present some next-to-leading order results on polarized
top quark decays which are analyzed in the top quark rest system.Comment: 11 pages, 4 figures, Invited talk given at the 12th Regional
Conference of Mathematical Physics, Islamabad, Pakistan, March 2006, to be
published in the proceeding
Helicity Amplitudes and Angular Decay Distributions
I discuss how to obtain angular decay distributions for sequential cascade
decays using helicity methods. The angular decay distributions follow from a
reasonably simple master formula involving bilinear forms of helicity
amplitudes and Wigner's functions. I discuss in some detail the issue of
gauge invariance for off-shell gauge bosons. As a technical exercise I
calculate the linear relation between the helicity amplitudes and the invariant
amplitudes of semileptonic and rare baryon decays. I discuss two explicit
examples of angular decay distributions for (i) the decay (which leads to the notion of the helicity fractions of the
), and (ii) the sequential decay .Comment: 16 pages, 2 figures, Lecture given at the Helmholtz International
Summer School "Physics of Heavy Quarks and Hadrons", Dubna, Russia, July
15--28, 2013 (to be published in the Proceedings
Effects of growth conditions on postharvest Botrytis infection in Gerbera - a nursery comparison
Botrytis cinerea is one of the main postharvest problems in gerbera cut flowers. There are clear differences among growers in the percentage of flowers showing symptoms of Botrytis infection after harvest. Because the factors causing these differences are uncertain, cultivation parameters of twelve different growers were followed and a nursery comparison was carried out. Gerbera flowers ‘Dino’ were sampled twelve times; six times in autumn 2006 and six times in spring of 2007. At the nurseries climate (air temperature, relative humidity, light intensity and CO2 concentration) was logged, and plant density, plant age and other characteristics were monitored. Before each harvest Botrytis spores were trapped in the greenhouses and counted. After sampling, flowers were treated according to a standard transport simulation. Thereafter Botrytis infection was monitored, and statistical analyses were performed on the effect of the pre-harvest conditions on Botrytis infection in the postharvest stage. Clear influence of the spore level in the greenhouse was observed. When a sufficient number of spores were present in the greenhouse environment, the humidity level and the intensity and duration of irradiation had the strongest influence on infection. In general, factors those lead to a dry microclimate such as the use of ventilators, the use of supplemental lighting and a low plant density were related with a lower number of lesions on gerbera petals in the postharvest phase
A Supersymmetric Model with the Gauge Symmetry SU(3)_1 X SU(2)_1 X U(1)_1 X SU(3)_2 X SU(2)_2 X U(1)_2
A supersymmetric model with two copies of the Standard Model gauge groups is
constructed in the gauge mediated supersymmetry breaking scenario. The
supersymmetry breaking messengers are in a simple form. The Standard Model is
obtained after first step gauge symmetry breaking. In the case of one copy of
the gauge interactions being strong, a scenario of electroweak symmetry
breaking is discussed, and the gauginos are generally predicted to be heavier
than the sfermions.Comment: 14 pages, revtex, 1 figure, messenger contents modified, discussion
on GUTs improve
Theory of Heavy Baryon Decay
We discuss various topics in the theory of heavy baryon decays. Among these
are recent applications of the Relativistic Three Quark Model to semileptonic,
nonleptonic, one-pion and one-photon transitions among heavy baryons, new
higher order perturbative results on the correlator of two heavy baryon
currents and on the semi-inclusive decay .Comment: 10 pages, invited talk given by J.G. K\"orner at the 3rd
International Conference on B Physics and CP Violation (BCONF99), Taipei,
Taiwan, 3-7 Dec 1999, to appear in the Proceedings, edited by H.Y. Cheng and
W.S. Hou (World Scientific, 2000
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