Claudio Corianò — Page 4

arXiv1995

$t$-Channel Unitarity Construction of Small-x Kernels

We present the BFKL equation as a reggeon Bethe-Salpeter equation and discuss the use of reggeon diagrams to obtain 2-2 and 2-4 reggeon interactions at $O(g^4)$. We 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. The derivation of gluon reggeization, the $O(g^2)$ BFKL kernel, and $O(g^4)$ corrections, is described within this formalism. We give an explicit expression for the $O(g^4)$ 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 $O(g^4)$ contributions from the multi-Regge effective action.

hep-ph↗

arXiv1993

Spectral Densities and Borel Transforms in Compton Scattering

We show that the leading double spectral density in sum rules for Compton-like processes can be obtained by simple properties of the Borel transform, extending an approach widely used in the literature on sum rules, and known to be valid only for the spectral densities of form factors. The extension is illustrated in the scalar case, where it is shown to be consistent with Cutkosky rules. Using arguments based on the analiticity properties of the vertex and the box diagrams, we show that Compton scattering is, however, a favourable case and indeed possible disagreements between the two methods are likely to be encountered in more general situations.

hep-ph↗