Minimal cascade decay of the top quark through a new scalar

We explore a possible decay of the top quark into a new scalar ${\phi }_t$ plus a charm quark. The decay is mediated by a dimension-5 operator that may be generated by the exchange of a heavy vectorlike quark, $\chi$, and can have a branching fraction close to a percent. In a minimal model, ${\phi }_t$ decays due to the same operator that allows the nonstandard top decay, leading to a final state involving a $c$ jet, a $b$ jet and a $W$ boson. Hence, the top quark would undergo a nonstandard cascade decay through ${\phi }_t$ and then through an off-shell top quark. The main nonstandard collider signal is a $t\bar{t}\to c\bar{c}b\bar{b}{W}^{+}{W}^{-}$ process. In addition, production of the vectorlike quark at the LHC would lead to a signal of the type $\chi {\phi }_{t}j\to 3c+b\bar{b}WWj$.