FCNC Decays of the Top Quark

Abstract

If new physics (e.g. SUSY) does not show up as direct evidence at the LHC, it could still be observable in FCNC processes involving the $t$-quark. We take a close look at the process $t\to c + h/Z$ and show that its branching ratio in the Standard Model is subject to three mechanisms of suppression. To obtain an observable signal, one needs to evade all these mechanisms in a theory beyond the Standard Model. We show that a theory like the cMSSM cannot provide a big enough enhancement. However, in a framework like $R$-parity-violating SUSY, observable signals are a distinct possibility.