QCD Amplitudes in the High-Energy Limit

Dijet production with a rapidity gap between the jets is considered as a test ground for the production of a heavy Higgs boson via weak-boson fusion at hadron supercolliders. It is argued that in order to perform a detailed analysis of dijet production with a rapidity gap we need an ${\cal O}(\al_s^4)$ calculation including the relevant collinear enhancements which give structure to the jets. Such a calculation needs not be exact, but must include the full leading power in $\hat{s}/\hat{t}$ of the rate of dijet production in the high-energy limit. The QCD amplitudes must be determined to the corresponding accuracy. Accordingly, the scattering amplitudes necessary to compute the full leading power in $\hat{s}/\hat{t}$ of dijet production to ${\cal O}(\al_s^3)$ are analysed.