Model independent predictions for rare top decays with weak coupling

Abstract

Measurements at $B$ factories have provided important constraints on new physics in several rare processes involving the $B$ meson. New physics, if present in the $b$ quark sector may also affect the top sector. In an effective Lagrangian approach, we write down operators, where effects in the bottom and the top sector are related. Assuming the couplings of the operators to be of the same size as the weak coupling $g$ of the standard model and taking into account constraints on new physics from the bottom sector as well as top branching ratios, we make predictions for the rare top decays $t\ensuremath{\rightarrow}cV$, where $V=\ensuremath{\gamma}$, $Z$. We find branching fractions for these decays within possible reach of the LHC. Predictions are also made for $t\ensuremath{\rightarrow}sW$.