Effective Lagrangian approach to Higgs-mediated flavor changing neutral current top quark decays

Abstract

The flavor changing neutral current (FCNC) transitions $t\ensuremath{\rightarrow}{q}^{\ensuremath{'}}H$ and $t\ensuremath{\rightarrow}{q}^{\ensuremath{'}}{V}_{i}$ $({V}_{i}=\ensuremath{\gamma},g,Z)$ are studied in the context of the effective Lagrangian approach. We focus on the scenario in which these decays are predominantly induced by new physics effects arising from the Yukawa sector extended with dimension-six ${\mathrm{S}\mathrm{U}}_{L}(2)\ifmmode\times\else\texttimes\fi{}{\mathrm{U}}_{Y}(1)$-invariant operators, which generate the most general $CP$-even and $CP$-odd $t{q}^{\ensuremath{'}}H$ vertex at the tree level. For the unknown coefficients, we assume a slightly modified version of the Cheng-Sher ansatz. We found that the branching ratio for the Higgs-mediated FCNC $t\ensuremath{\rightarrow}{q}^{\ensuremath{'}}{V}_{i}$ decays are enhanced by two or 3 orders of magnitude with respect to the results expected in models with extended Higgs sectors, such as the general two-Higgs doublet model. We discuss the possibilities of detecting this class of decays at the large hadron collider (LHC).