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 $q \bar q \rightarrow q \bar q gg \cdots g$ in the like-helicity gluon case.Comment: 80 pages, 2 figures (appended in pictex), CLNS 91/112

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

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 $n$ 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 $Z$ or neutrino pairs.Comment: 73 pages, 2 figures (appended in pictex), CLNS 92/115

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

Multiple Interactions in Two-Photon Collisions

We compute cross sections for events where two pairs of partons scatter off each other in the same $\gamma\gamma$ reaction, giving rise to at least 3 high--{\mbox{$p_T^{}$}} jets. Unlike in {\mbox{$p \bar p$}}\ collisions we find the signal to lie well above the background from higher order QCD processes. If the usual ``eikonaliztion" assumption is correct, the signal should be readily observable at LEP2, and might already be detectable in data taken at TRISTAN.Comment: 8 pages, plain LaTeX, 2 figures (not included). A compressed PS file of the entire paper, including figures, can be obtained via anonymous ftp from ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-921.ps.

Next-to-Maximal Helicity Violating Amplitudes in Gauge Theory

Using the novel diagrammatic rules recently proposed by Cachazo, Svrcek, and Witten, I give a compact, manifestly Lorentz-invariant form for tree-level gauge-theory amplitudes with three opposite helicities.Comment: 12 pages, 1 figur