1,111 research outputs found
Generalized Gluon Currents and Applications in QCD
We consider the process containing two quark lines and an arbitrary number of
gluons in a spinor helicity framework. A current with two off-shell gluons
appears in the amplitude. We first study this modified gluon current using
recursion relations. The recursion relation for the modified gluon current is
solved for the case of like-helicity gluons. We apply the modified gluon
current to compute the amplitude for in the like-helicity gluon case.Comment: 80 pages, 2 figures (appended in pictex), CLNS 91/112
Multiphoton Production at High Energies in the Standard Model I
We examine multiphoton production in the electroweak sector of the Standard
Model in the high energy limit using the equivalence theorem in combination
with spinor helicity techniques. We obtain recursion relations for currents
consisting of a charged scalar, spinor, or vector line that radiates
photons. Closed form solutions to these recursion relations for arbitrary
are presented for the cases of like-helicity and one unlike-helicity photon
production. We apply the currents singly and in pairs to obtain amplitudes for
processes involving the production of photons with up to two unlike
helicities from a pair of charged particles. The replacement of one or more
photons by transversely polarized Z$-bosons is also discussed.Comment: 75 pages, CLNS 91/111
Weyl-van-der-Waerden formalism for helicity amplitudes of massive particles
The Weyl-van-der-Waerden spinor technique for calculating helicity amplitudes
of massive and massless particles is presented in a form that is particularly
well suited to a direct implementation in computer algebra. Moreover, we
explain how to exploit discrete symmetries and how to avoid unphysical poles in
amplitudes in practice. The efficiency of the formalism is demonstrated by
giving explicit compact results for the helicity amplitudes of the processes
gamma gamma -> f fbar, f fbar -> gamma gamma gamma, mu^- mu^+ -> f fbar gamma.Comment: 24 pages, late
The Analysis of Multijet Events Produced at High Energy Hadron Colliders
We define and discuss a set of (4N - 4) parameters that can be used to
analyse events in which N jets have been produced in high energy hadron-hadron
collisions. These multijet variables are the multijet mass and (4N - 5)
independent dimensionless parameters. To illustrate the use of the variables
QCD predictions are presented for events with up to five jets produced at the
Fermilab Tevatron Proton-Antiproton Collider. These QCD predictions are
compared with the predictions of a model in which multijet events uniformly
populate the N-body phase-space
Charge asymmetry in hadroproduction of heavy quarks
A sizeable difference in the differential production cross section of top and
antitop quarks, respectively, is predicted for hadronically produced heavy
quarks. It is of order and arises from the interference between
charge odd and even amplitudes respectively. For the TEVATRON it amounts to
approximately 5-10% in the region where the cross section is large and could
therefore be measured in the next round of experiments. At the LHC the
asymmetry can be studied by selecting appropriately chosen kinematical regions.Comment: LaTeX, 5pp, 5 figures, uses revtex. The complete paper, including
figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/ Final version as
published in Phys.Rev.Let
Detection of Neutral MSSM Higgs Bosons at LEP-II and NLC
We study the possibility of detecting the neutral Higgs bosons predicted in
the Minimal Supersymmetric Standard Model (h0, H0, A0), with the reactions e+
e- --> b b h0 (H0, A0), using the helicity formalism. We analyze the region of
parameter space (m_A0-tan beta) where h0(H0, A0) could be detected in the limit
when tan beta is large. The numerical computation is done for the energy which
is expected to be available at LEP-II (sqrt{s} = 200 GeV) and for a possible
Next Linear e+ e- Collider (sqrt{s}=500 GeV).Comment: To be published in Phys.Rev.
Multiphoton Production at High Energies in the Standard Model II
We examine multiphoton production in the electroweak sector of the Standard
Model in the high energy limit using the equivalence theorem in combination
with spinor helicity techniques. We utilize currents consisting of a charged
scalar, spinor, or vector line that radiates photons. Only one end of the
charged line is off shell in these currents, which are known for the cases of
like-helicity and one unlike-helicity photons. We obtain a wide variety of
helicity amplitudes for processes involving two pairs of charged particles by
considering combinations of four currents. We examine the situation with
respect to currents which have both ends of the charged line off-shell, and
present solutions for the case of like-helicity photons. These new currents may
be combined with two of the original currents to produce additional amplitudes
involving Higgs, longitudinal or neutrino pairs.Comment: 73 pages, 2 figures (appended in pictex), CLNS 92/115
Amplitudes With Different Helicity Configurations Of Noncommutative QED
The amplitudes of purely photonic and photon{2-fermion processes of non-
commutative QED (NCQED) are derived for different helicity configurations of
photons. The basic ingredient is the NCQED counterpart of Yang-Mills recursion
relations by means of Berends and Giele. The explicit solutions of recursion
relations for NCQED photonic processes with special helicity configurations are
presented.Comment: 23 pages, 2 figure
Quantum Corrections to the Reissner-Nordstrom and Kerr-Newman Metrics: Spin 1
A previous evaluation of one-photon loop corrections to the energy-momentum
tensor has been extended to particles with unit spin and speculations are
presented concerning general properties of such forms.Comment: 21 pages, 1 Figur
Special case of sunset: reduction and epsilon-expansion
We consider two loop sunset diagrams with two mass scales m and M at the
threshold and pseudotreshold that cannot be treated by earlier published
formula. The complete reduction to master integrals is given. The master
integrals are evaluated as series in ratio m/M and in epsilon with the help of
differential equation method. The rules of asymptotic expansion in the case
when q^2 is at the (pseudo)threshold are given.Comment: LaTeX, 13 pages, 1 figur
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