Interference effects for the top quark decays t → b+W+/H+(→τ+ντ)

Applying Applying the narrow-width approximation, we first review the next-to-leading-order QCD predictions for the total decay rate of a top quark considering two unstable intermediate particles: the W+ boson in the standard model of particle physics and the charged Higgs boson H in the generic type-I and-II two Higgs -doublet models, i.e., t -> b+W+/H+(->tau+nu(tau)). We then estimate the errors that arise from this approximation at leading-order perturbation themy. Finally, we investigate the interference effects in the factorization of production and decay parts of intermediate particles. We will show that for nearly mass degenerate states (m(H+) approximate to m(W+)H) the correction due to the interference effect is considerable.