Top-quark flavor-changing tqZ couplings and rare Δ F= 1 processes

Chuan Hung Chen, Takaaki Nomura

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1 Citation (Scopus)


We study the impacts of anomalous tqZ couplings (q= u, c), which lead to the t→ qZ decays, on low energy flavor physics. It is found that the tuZ-coupling effect can significantly affect the rare K and B decays, whereas the tcZ-coupling effect is small. Using the ATLAS’s branching ratio (BR) upper bound of BR(t→ uZ) < 1.7 × 10 - 4, the influence of the anomalous tuZ-coupling on the rare decays can be found as follows: (a) The contribution to the Kaon direct CP violation can be up to Re(ϵ/ ϵ) ≲ 0.8 × 10 - 3; (b) BR(K+→ π+νν¯) ≲ 12 × 10 - 11 and BR(KL→ πνν¯) ≲ 7.9 × 10 - 11; (c) the BR for KS→ μ+μ- including the long-distance effect can be enhanced by 11 % with respect to the standard model result, and (d) BR(Bd→ μ+μ-) ≲ 1.97 × 10 - 10. In addition, although Re(ϵ/ ϵ) cannot be synchronously enhanced with BR(KL→ πνν¯) and BR(KS→ μ+μ-) in the same region of the CP-violating phase, the values of Re(ϵ/ ϵ) , BR(K+→ π+νν¯) , and BR(Bd→ μ+μ-) can be simultaneously increased.

Original languageEnglish
Article number644
JournalEuropean Physical Journal C
Issue number8
Publication statusPublished - 2019 Aug 1

All Science Journal Classification (ASJC) codes

  • Engineering (miscellaneous)
  • Physics and Astronomy (miscellaneous)


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