A Simulation of QCD Radiation in Top Quark Decays
  In this paper we describe a theoretical framework and algorithms for implementing QCD corrections to top quark decays in the Herwig++ event generator. The dominant corrections, due to soft and collinear emissions, are summed to all orders through the coherent parton branching formalism. In addition, unenhanced first-order matrix-element corrections are included to account for large transverse momentum emissions. 
Keith Hamilton and Peter Richardson