A. Djouadi

Higgs bosons: Intermediate mass range at e+e- colliders.

We elaborate on the production of the standard model Higgs particle at high-energy [ital e][sup +][ital e[minus]] colliders through the reaction [ital e][sup +][ital e[minus]][r arrow][ital ZH]. Particular emphasis is put on the intermediate mass range. In addition to the signal we discuss in detail the background processes. Angular distributions which are sensitive to the spin and parity of the Higgs particle are analyzed.

Leading electroweak correction to Higgs boson production at proton colliders

At proton colliders, Higgs particles are dominantly produced in the gluon-gluon fusion mechanism. The Higgs-boson--gluon coupling is mediated by heavy quark loops, and the process can serve to count the number of heavy strongly interacting particles whose masses are generated by the Higgs mechanism. We present the two-loop leading electroweak radiative correction to this coupling, which is quadratically proportional to the heavy quark masses. It turns out that this correction is well under control across the physically interesting quark mass ranges.

QCD corrections to scalar quark pair production in

We calculate the QCD rediative corrections to the production of the supersymmetric scalar partners of quarks in {ital e}{sup +}{ital e}{sup {minus}} annihilation. We include both the standard gluonic corrections and the genuine supersymmetric QCD corrections due to quark-gluino loops, and allow for mixing between left- and right-handed scalar quarks which leads to the possibility that the two final state particles have different masses. The corrections are found to be much larger than the ones affecting the production of spin-1/2 particles.

e^{+} e^{-}

We calculate supersymmetric QCD corrections (squark and gluino loops) to quark pair production in [ital e][sup +][ital e[minus]] annihilation, allowing for mixing between left- and right-handed squarks and taking into account the effects of nonzero quark masses. Corrections to the [ital Z] boson partial widths are generally small and positive, except in the case of large [ital [tilde b]] squark mixing, where they become negative. At high-energy [ital e][sup +][ital e[minus]] colliders, larger corrections to the total cross sections are possible. Corrections to forward-backward asymmetries are negligible except possibly for top quarks, where they are sensitive to [ital [tilde t]] squark mixing. We also comment on the possibility that the gluino mass is only a few GeV.

annihilation

We derive the QCD corrections to the electroweak gauge boson vacuum polarization functions at high and zero momentum transfer in the case of arbitrary internal quark masses. We then discuss in this general case (i) the connection between the [ital O]([alpha][alpha][sub [ital s]]) calculations of the vector boson self-energies using dimensional regularization and the one performed via a dispersive approach and (ii) the QCD corrections to the [rho] parameter for a heavy quark isodoublet.

Supersymmetric QCD corrections to quark pair production in e+e- annihilation.

We calculate the decay rate of scalar and pseudoscalar Higgs bosons into a pair of gluinos, within the Minimal Supersymmetric Standard Model. In the theoretically and experimentally allowed light gluino window, m˜ ∼ 3–5 GeV, gluino pairs can completely dominate the decays of the light scalar Higgs boson and play a prominent role in the decay of the pseudoscalar Higgs boson. This would alter the limits obtained from Z decays on the lightest CP–even and CP–odd Higgs bosons, and could jeopardize the search for these Higgs particles at future hadron colliders. In contrast, the branching ratio for the two–body decay of Z bosons into pairs of light gluinos is less than 0.1%.