Decay of the charged Higgs boson and the top quark in two-Higgs-doublet model at NNLO in QCD

We present numerical calculations of the partial width of the charged Higgs boson decay into a top quark, H- (t) over bar + b+ X, and the partial width of the top quark decay into a light charged Higgs boson t -> H++ b+ X at next-to-next-to-leading order (NNLO) in QCD, based on a factorization formula of the jet mass. The NNLO corrections significantly reduce the renormalization scale dependence of the partial decay width in both cases. We show relative size of the NNLO corrections for different charged Higgs boson masses and for different renormalization scales. The NNLO corrections are about 16% (1%) of the leading order widths for the charged Higgs boson mass of 200 GeV (2000 GeV), while it is quite small for the top quark decay. Our analyses are independent of the detailed structure of the Yukawa couplings, and can be applied to various new physics models, as demonstrated by the decay branching ratio in different types of the two-Higgs-doublet models.