Compactified five dimensional Yang-Mills theory results in an effective four-dimensional theory with a Kaluza-Klein (KK) tower of massive vector bosons. We explicitly demonstrate that the scattering of the massive vector bosons is unitary at tree-level for low energies, and analyze the relationship between the unitarity violation scale in the KK theory and the nonrenormalizability scale in the five dimensional gauge theory. In the compactified theory, low-energy unitarity is ensured through an interlacing cancellation among contributions from the relevant KK levels. Such cancellations can be understood using a Kaluza-Klein equivalence theorem which results from the geometric "Higgs" mechanism of compactification. In these theories, the unitarity violation is delayed to energy scales higher than the customary limit through the introduction of additional vector bosons rather than Higgs scalars.

We calculate the changes in the yields of primordial nucleosynthesis which result from small corrections to rates for weak processes that connect neutrons and protons. We correct the weak rates by improved treatment of Coulomb and radiative corrections, and by inclusion of plasma effects. Our calculations lead to a systematic decrease in the predicted 4He abundance of about AY=O.0025. The relative changes in other primordial abundances are also 1-2%.

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We show that heavy-quark production via W-gluon fusion in high-energy pp and pp collisions is an important source of the heavier member of an SU(2jL doublet of quarks if the mass splitting within the doublet is large. W-gluon fusion exceeds the strong production of heavy quarks for mass splittings greater than 300-350 GeV at 6 = 10 TeV and 400-450 GeV at 6 =40 TeV. An alternative way to regard W-gluon fusion is as the production of the heavier quark by fusing its light partner with a W boson. We use a distribution function for the light partner to show that this process gives results which agree qualitatively with W-gluon fusion. We also discuss the Drell-Yan production of an SU(2)r doublet of heavy quarks via a virtual W boson and corrections to this process from initial gluons. We find that at the Fermilab Tevatron energy 6 =2 TeV, W-gluon fusion exceeds the Drell-Yan production of top quarks for masses above 100 GeV.

We argue that the leading-order subprocess for Higgs-boson production in association with bottom quarks is bb → H. This process is an important source of Higgs bosons with enhanced Yukawa coupling to bottom quarks. We calculate the corrections to this cross section at next-to-leading-order in 1/ ln(m H /m b ) and α s and at next-to-next-to-leading order in 1/ ln(m H /m b ).