Top-quark rare decays with flavor violation

In the present study,we investigated the decays of the top quark:t→cy,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 proccsscs,i.e.,t→cγ,cg,cZ,ch,can reach the same order of magnitude as their experimental upper limits.Among them,tanβ has the most evident effect on these processes and is the main parameter;gX,gYX,μ,M2,λH,MU232,and MQ232 are also important parameters for the processes,and have effects on the numerical results.