Effective Lagrangian Approach to Top Decay via Flavor Changing Neutral Current

Abstract

We study possible non-standard $tuZ$ and $tcZ$ couplings, which induce flavor-changing neutral-current decays of the top quark, in the effective-Lagrangian framework. The corresponding interaction Lagrangian comes from several $SU(3)\times SU(2)\times U(1)$ invariant dimension-6 effective operators, and it includes four independent complex-number coupling constants. Constraints on those non-standard coupling constants in each interaction are derived by using the present experimental limits of the branching fractions for $t\to uZ$ and $t\to cZ$ processes. Expected improvements of the constraints at future facilities are discussed as well. It is also pointed out that some correlations hold among those constrained coupling constants.

Comments: 4 pages, 1 figure, 2 tables, Contribution to the Proceedings of the XXIX International Symposium on Lepton Photon Interactions at High Energies - LeptonPhoton2019, 5-10 August 2019, Toronto, Canada