  The computation of exclusive QCD jet observables at higher orders requires a
method for the subtraction of infrared singular configurations arising from
multiple radiation of real partons. One commonly used method at next-to-leading
order (NLO) is based on the antenna factorization of colour-ordered matrix
elements, and uses antenna functions to subtract the real radiation
singularities. Up to now, NLO antenna functions could be derived in a
systematic manner only for hard quark-antiquark pairs, while the gluon-gluon
and quark-gluon antenna functions were constructed from their limiting
behaviour. In this paper, we show that antenna functions for hard quark-gluon
pairs can be systematically derived from an effective Lagrangian describing
heavy neutralino decay. The infrared structure of the colour-ordered neutralino
decay matrix elements at NLO and NNLO is shown to agree with the structure
observed for parton radiation off a quark-gluon antenna.
