189 research outputs found
Looking Beyond the Standard Model through Precision Electroweak Physics
The most important hint of physics beyond the Standard Model (SM) from the
1995 precision electroweak data is that the most precisely measured quantities,
the total, leptonic and hadronic decay widths of the and the effective weak
mixing angle, , measured at LEP and SLC, and the quark-lepton
universality of the weak charged currents measured at low energies, all agree
with the predictions of the SM at a few level. By taking into
account the above constraints I examine implications of three possible
disagreements between experiments and the SM predictions. It is difficult to
interpret the 11\% (2.5-) deficit of the -partial-width ratio
, since it either implies an unacceptably large
or a subtle cancellation among hadronic decay widths in order to
keep all the other successful predictions of the SM. The 2\% (3-)
excess of the ratio may indicate the presence of a new
rather strong interaction, such as the top-quark Yukawa coupling in the
supersymmetric (SUSY) SM or a new interaction responsible for the large
top-quark mass in the Technicolor scenario of dynamical electroweak symmetry
breaking. Another interpretation may be additional tree-level gauge
interactions that couple only to the third generation of fermions. A common
consequence of these attempts is a rather small , \alpha_s(\mz
)_{\msbar}=0.104\pm 0.08. The 0.17\% (1-) deficit ...Comment: Talk presented at Yukawa International Seminar (YKIS)~'95, 23 pages,
uuencoded compressed tar file of LaTeX file and 13 EPS files (uses
ptptex.sty,wrapfig.sty,psfig.sty,axodraw.sty) PostScript version of complete
paper available at ftp://ftp.kek.jp/kek/preprints/TH/TH-463/kekth463.ps.g
Generating QCD amplitudes in the color-flow basis with MadGraph
We propose to make use of the off-shell recursive relations with the
color-flow decomposition in the calculation of QCD amplitudes on MadGraph. We
introduce colored quarks and their interactions with nine gluons in the
color-flow basis plus an Abelian gluon on MadGraph, such that it generates
helicity amplitudes in the color-flow basis with off-shell recursive formulae
for multi-gluon sub-amplitudes. We demonstrate calculations of up to 5-jet
processes such as , and
. Although our demonstration is limited, it paves the way
to evaluate amplitudes with more quark lines and gluons with Madgraph.Comment: 29 pages, 13 figure
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