1,061 research outputs found
Production of a Higgs pseudoscalar plus two jets in hadronic collisions
We consider the production of a Higgs pseudoscalar accompanied by two jets in
hadronic collisions. We work in the limit that the top quark is much heavier
than the Higgs pseudoscalar and use an effective Lagrangian for the
interactions of gluons with the pseudoscalar. We compute the amplitudes
involving: 1) four gluons and the pseudoscalar, 2) two quarks, two gluons and
the pseudoscalar and 3) four quarks and the pseudoscalar. We find that the
pseudoscalar amplitudes are nearly identical to those for the scalar case, the
only differences being the overall size and the relative signs between terms.
We present numerical cross sections for proton-proton collisions with
center-of-mass energy 14 TeV.Comment: 12 pages, LaTeX, 4 Postscript figures, submitted to Phys. Rev.
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
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
Standard Model Top Quark Asymmetry at the Fermilab Tevatron
Top quark pair production at proton-antiproton colliders is known to exhibit
a forward-backward asymmetry due to higher-order QCD effects. We explore how
this asymmetry might be studied at the Fermilab Tevatron, including how the
asymmetry depends on the kinematics of extra hard partons. We consider results
for top quark pair events with one and two additional hard jets. We further
note that a similar asymmetry, correlated with the presence of jets, arises in
specific models for parton showers in Monte Carlo simulations. We conclude that
the measurement of this asymmetry at the Tevatron will be challenging, but
important both for our understanding of QCD and for our efforts to model it.Comment: 26 p., 10 embedded figs., comment added, version to appear in PR
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
Infrared behavior of graviton-graviton scattering
The quantum effective theory of general relativity, independent of the
eventual full theory at high energy, expresses graviton-graviton scattering at
one loop order O(E^4) with only one parameter, Newton's constant. Dunbar and
Norridge have calculated the one loop amplitude using string based techniques.
We complete the calculation by showing that the 1/(d-4) divergence which
remains in their result comes from the infrared sector and that the cross
section is finite and model independent when the usual bremsstrahlung diagrams
are included.Comment: 12 pages, uses axodra
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
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