$ O(\alpha_s) $ corrections to polarized top decay into a charged Higgs   $ t(\uparrow) \to H^+ + b $
  We calculate the $ O(\alpha_s) $ radiative corrections to polarized top quark decay into a charged Higgs boson and a massive bottom quark in two variants of the two-Higgs-doublet model. The radiative corrections to the polarization asymmetry of the decay may become as large as $ 25 % $. We provide analytical formulae for the unpolarized and polarized rates for $ m_b \neq 0 $ and for $ m_b = 0 $. For $ m_b = 0 $ our closed-form expressions for the unpolarized and polarized rates become rather compact. 
A. Kadeer, J.G. K\"orner, M.C. Mauser