Abstract
Abstract
The observed flavor-changing neutral-current (FCNC) processes in the standard model (SM) arise from the loop diagrams involving the weak charged currents mediated by the W-gauge boson. Nevertheless, the top-quark FCNCs and lepton flavor-violating processes resulting from the same mechanism are highly suppressed. We investigate possible new physics effects that can enhance the suppressed FCNC processes, such as a top quark decaying into a light quark with a Higgs or gauge boson in the final state, i.e. t → q(h, V) with V = γ, Z, g,
h
→
ℓ
ℓ
′
, and
ℓ
→
ℓ
′
γ
. To achieve the assumption that the induced FCNCs are all from quantum loops, we consider the scotogenic mechanism, where a Z
2 symmetry is introduced and only new particles carry an odd Z
2 parity. With the extension of the SM to include an inert Higgs doublet, an inert charged Higgs singlet, a vector-like singlet quark, and two neutral leptons, it is found that, with relevant constraints taken into account, the t → c(h, Z), h → μ
τ, and τ → ℓ
γ decays can be enhanced up to the expected sensitivities in experiments. The branching ratios of h → μ
+
μ
−/τ
+
τ
− from only new physics effects can reach up to
O
(
10
−
3
)
. Intriguingly, the resulting muon g − 2 can fit the combined data within 2 standard deviations, whereas the electron g − 2 can have either sign with a magnitude of
O
(
10
−
13
−
10
−
12
)
. In addition, we examine the oblique parameters in the model and find that the resulting W-mass anomaly observed by CDF II can be accommodated.