Probing new physics from top quark FCNC processes at linear colliders: a mini review

We briefly review the studies on the top quark FCNC (flavor-changing neutral-current) processes at linear colliders. Such processes, including various FCNC top quark rare decays and top-charm associated productions, are extremely suppressed in the standard model (SM) but could be significantly enhanced in some extensions. We compared the predictions of different typical physics models: the SM, the minimal supersymmetric model (MSSM), the general two-higgs-doublet model (2HDM) and the topcolor-assisted technicolor (TC2) model. Our findings are: (1) While all the new physics models can enhance the rates by several orders relative to the SM predictions, the TC2 model predicts much larger rates than other models; (2) The optimal channel for probing the top quark FCNC is the top-charm associated production in γγ collision, which occurs at a much higher rate than in e+e- or e-γ collision, and can reach the detectable level for a large part of the parameter space. (author)