Top-quark rare decays with flavor violation

In the present study, we investigated the decays of the top quark: t -> c gamma, t -> cg, t -> cZ, and t -> ch. They are extremely rare processes in the standard model (SM). As the U(1) extension of the minimal supersymmetric standard model (MSSM), the U(1)(X) 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., t -> c gamma, cg, cZ, ch, can reach the same order of magnitude as their experimental upper limits. Among them, tan beta has the most evident effect on these processes and is the main parameter; gX, gYX, mu, M-2, lambda H, MU232, and M-Q23(2) are also important parameters for the processes, and have effects on the numerical results.