Top-quark rare decays with flavor violation*

In the present study, we investigated the decays of the top quark: , , , and . They are extremely rare processes in the standard model (SM). As the extension of the minimal supersymmetric standard model (MSSM), the SSM features new superfields such as the right-handed neutrinos and three Higgs singlets. We analyzed the effects of different sensitive parameters on the results and made reasonable theoretical predictions, thereby providing a useful reference for future experimental development. Considering the constraint set by the updated experimental data, the numerical results show that the branching ratios of the four processes, i.e., , can reach the same order of magnitude as their experimental upper limits. Among them, has the most evident effect on these processes and is the main parameter; , , , , , , and are also important parameters for the processes, and have effects on the numerical results.