SUSY-Induced Top Quark FCNC Processes at Linear Colliders

In the Minimal Supersymmetric Model (MSSM) the hitherto unconstrained flavor mixing between top-squark and charm-squark will induce the flavor-changing neutral-current (FCNC) interaction between top quark and charm quark, which then give rise to various processes at the next generation linear collider (NLC), i.e., the top-charm associated productions via $e^+ e^-$, $e^- \gamma$ and $\gamma \gamma$ collisions as well as the top quark rare decays $t \to c V$ ($V=g$, $\gamma$ or $Z$). All these processes involve the same part of the parameter space of the MSSM. Through a comparative analysis for all these processes at the NLC, we found the best channel to probe such SUSY-induced top quark FCNC is the top-charm associated production in $\gamma \gamma$ collision, which occurs at a much higher rate than $e^+ e^-$ or $e^- \gamma$ collision and may reach the detectable level for some part of the parameter space. Since the rates predicted by the Standard Model are far below the detectable level, the observation of such FCNC events would be a robust indirect evidence of SUSY.