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.
Highlights
Since the discovery in 1995 by the CDF and D0 experiments at the ppcollider Tevatron at Fermilab, the top quark has been at or near the center of attention in high-energy physics
A lot of theoretical work has gone into firming up the cross sections for the tt pair and the single top production at the Tevatron and the LHC, undertaken in the form of higherorder QCD corrections [1,2,3,4]
It is shown that this decay mode can reach a sizable branching fraction at low tan β once it is kinematically permitted. These results show that the exotic decay channel Hþ → AWþ=HWþ is complementary to the conventional Hþ → τþντ channel considered in the current minimal supersymmetric standard model (MSSM) scenarios
Summary
Since the discovery in 1995 by the CDF and D0 experiments at the ppcollider Tevatron at Fermilab, the top quark has been at or near the center of attention in high-energy physics. Improved theoretical calculations of the top quark decay width and distributions started a long time ago In this regard, the leading-order perturbative QCD corrections to the lepton energy spectrum in the decays t → bWþ → bðlþνlÞ were calculated some 30 years ago [5]. [22,23], the OðαsÞ QCD corrections to the hadronic decay width of a charged Higgs boson, i.e., Γðt → bHþÞ, are calculated, and in Ref. Since the main contribution to the top quark decay mode (1) comes from the kinematic region where the Wþ boson is near its mass shell, one has to take into account its finite decay width ΓW. In Eq (3), we employ the Breit-Wigner prescription of the Wþ-boson propagator for which the propagator contribution of an unstable particle of mass MW and total width ΓW is given by p2W
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