t-Channel unitarity construction of small-x kernels

In the leading-log approximation, the small-x behavior of parton distributions in QCD is derived from the BFKL evolution equation. The authors describe the ion as a reggeon Bethe-Salpeter equation and discuss the use of reggeon diagrams to obtain 2-2 and 2-4 reggeon interactions at O(g{sup 4}). They then outline the dispersion theory basis of multiparticle j-plane analysis and describe how a gauge theory can be studied by combining Ward identity constraints with the group structure of reggeon interactions. Gluon reggeization, the O(g{sup 2}) BFKL kernel and O(g{sup 4}) corrections to it, are derived within this formalism. They give an explicit expression for the O(g{sup 4}) forward ``parton`` kernel in terms of logarithms and evaluate the eigenvalues. A separately infra-red finite component with a holomorphically factorizable spectrum is shown to be present and conjectured to be a new leading-order partial-wave amplitude. A comparison is made with Kirschner`s discussion of O(g{sup 4}) contributions from the multi-Regge effective action