Effective Lagrangian Approach to Top Decay via Flavor Changing Neutral Current

TL;DR

This paper investigates non-standard flavor-changing neutral current couplings in top quark decays using an effective Lagrangian framework, deriving current constraints and discussing future experimental improvements.

Contribution

It introduces a comprehensive effective Lagrangian model for top FCNC decays and derives constraints on its parameters from current and future experimental data.

Findings

Current experimental limits constrain non-standard couplings.

Future experiments could tighten these constraints.

Correlations among coupling constants are identified.

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 $t \to u Z$ and $t \to c Z$ 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.