# Interference effects for the top quark decays $t\to b+W^+/H^+(\to\tau^+\nu_\tau)$

## TL;DR

This paper reviews NLO QCD predictions for top quark decays involving W and charged Higgs bosons, estimates errors from the narrow-width approximation, and investigates interference effects, especially for nearly degenerate masses.

## Contribution

It provides a detailed analysis of interference effects in top quark decays with nearly degenerate intermediate particles, extending previous models.

## Key findings

- Interference effects are significant when $m_{H^+} \
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## Abstract

Applying the narrow-width approximation (NWA), we first review the NLO QCD predictions for the total decay rate of top quark considering two unstable intermediate particles: the $W^+$-boson in the standard model (SM) of particle physics and the charged Higgs boson $H^+$ in the generic type-I and II two-Higgs-doublet models, i.e. $t\to b+W^+/H^+(\to \tau^+\nu_\tau)$. We then estimate the errors arised from this approximation at leading-order perturbation theory. Finally, we shall investigate the interference effects in the factorization of production and decay parts of intermediate particles. We will show that for nearly mass-degenerate states ($m_{H^+}\approx m_{W^+}$), the correction due to the interference effect is considerable.