https://doi.org/10.1140/epjc/s10052-019-7133-5
Regular Article - Theoretical Physics
Top-quark flavor-changing tqZ couplings and rare 
processes
1
Department of Physics, National Cheng-Kung University, Tainan, 70101, Taiwan
2
School of Physics, KIAS, Seoul, 02455, Republic of Korea
* e-mail: nomura@kias.re.kr
Received:
10
March
2019
Accepted:
12
July
2019
Published online:
7
August
2019
We study the impacts of anomalous tqZ couplings (
), which lead to the 
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 
, 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 
; (b) 
and 
; (c) the BR for 
including the long-distance effect can be enhanced by 
with respect to the standard model result, and (d) 
. In addition, although 
cannot be synchronously enhanced with 
and 
in the same region of the CP-violating phase, the values of , 
, and 
can be simultaneously increased.
© The Author(s), 2019
