  The flavor changing neutral current (FCNC) transitions t --> q'H and t -->
q'V_i (V_i=\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 SU_L(2) X U_Y(1)-invariant operators, which generate the most
general CP-even and CP-odd tq'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--> q'V_i decays
are enhanced by two or three 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 LHC.
