Four-jet decays of theZ 0: Prospects of testing the triple gluon coupling

A large fraction of 4-jet events inZ ⁰ decays evolve fromq \(\bar q\) gg parton states. These configurations allow us to test the triple gluon coupling which is a consequence of the non-Abelian nature of QCD. The strength and the form of this coupling determine the quark-gluon decomposition of the final state as well as angular correlations between the jets. A critical assessment of the sensitivity of these observables to theggg vertex is presented under realistic experimental conditions. Methods to improve the sensitivity in large samples ofZ ⁰ decays are suggested.     

The three-gluon vertex of QCD

We show how the Q² evolution of gluon jets can be used to provide indirect but strong evidence for the three-gluon vertex of QCD. We propose looking for this evolution in the $Q\overline{Q}\to 3G\to$ hadrons decay of successive 1 ³S₁ quarkonium states. The results apply to other processes if G-jets can be isolated.     

Signatures of neutral heavy leptons in neutrino-induced dilepton events

The tentative indication in some experiments of μ^?e⁺ or π^?μ⁺ events with unusual characteristics revives the speculation that neutrino-induced dileptons may contain a weak signal of neutral heavy lepton (L⁰) production. We study the characteristics of dileptons expected from the production of an L⁰ through a current of the form $\text{L}{}^0\text{γ}{}_{\mathrm{\alpha }}\text{(1+γ}{}_5\text{)ν}{}_{\mathrm{\mu }}$. Both quasi-elastic and deep inelastic excitation are investigated and a comparison is made with dileptons of charm origin. As an illustration of a model with a ν_μ→L⁰ transition, we discuss the 2-2 version of the SU(2) × U(1) model and comment on the role of the Higgs particle in such transitions.     

The extended Higgs system in R-symmetric supersymmetry theories

The Higgs sector is extended in R  -symmetric supersymmetry theories by two iso-doublets R_d,u$R_{d,u}$ which complement the standard iso-doublets H_d,u$H_{d,u}$. We have analyzed masses and interactions of these novel states and describe their [non-standard] decay modes and their production channels at the LHC and e⁺e⁻$e^{+}{e}^{-}$ colliders.     

Stop decays in SUSY-QCD

The partial widths are determined for stop decays to top quarks and gluinos, and gluino decays to stop particles and top quarks (depending on the masses of the particles involved). The widths are calculated including one-loop SUSY-QCD corrections. The radiative corrections for these strong-interaction decays are compared with the SUSY-QCD corrections for electroweak stop decays to quarks and neutralinos/charginos and top-quark decays to stops and neutralinos.     

Formation and decay of scalar Leptoquarks/Squarks in ep collisions

The cross sections for the formation of scalar resonances, leptoquarks or squarks, in electron/positron-proton collisions at HERA are presented, including next-to-leading order QCD corrections. Depending mildly on the mass of the resonances, the K-factors increase the production cross sections by up to 30% if the target quarks are valence quarks. The QCD corrections to the partial decay widths of leptoquarks/ squarks to leptons and quarks are small. The electron spectrum in the decays is nevertheless softened by perturbative gluon radiation at a level of 2 GeV for a leptoquark/ squark mass of 200 GeV.     

Exploring the SUSY Higgs sector ate +e− linear colliders: a synopsis

We discuss the Higgs scenario in the minimal supersymmetric extension of the Standard Model ate ⁺e^? linear colliders operating in the c.m. energy range between 300 and 500 GeV. Besides decays of the Higgs particles into ordinary fermions and cascade decays, we analyze also decays into gaugino/Higgsinos and in particular, neutral Higgs decays into the lightest supersymmetric particles which are invisible ifR-parity is conserved. The cross sections for the various production channels of SUSY Higgs particles ine ⁺e^? collisions are discussed in detail. The lightest Higgs boson cannot escape detection, and in major parts of the MSSM parameter space all five Higgs particles can be observed.     

Signals of excited quarks and leptons

e⁺e^? annihilation to two photons (including beam polarization) and quark-antiquark annihilation to gluons are discussed as possible tools to investigate the existence (and handedness) of excited electrons and quarks. Properties of these particles can also be explored in eγ and ep colliders; production cross sections and the impact of these particles on structure functions are derived.     

Three-jet distributions ine + e − annihilation: Electromagnetic and weak production

Hard gluon bremsstrahlung off quarks ine ⁺ e ^? annihilation is expected to produce three-jet events. The angular distributions of the jets are calculated for electromagnetic and weak production in the high energy region (Z resonance decay included). Numerical estimates are presented for the vectoraxialvector interference terms within the Weinberg-Salam theory. We discuss (i) angular correlations between jets, (ii) semiinclusive pion distributions and (iii) we comment on angular asymmetries of leptons originating from heavy quark decays.