A Study on Top Quark FCNC Interactions in SMEFT Framework

Abstract

We present a model-independent study of rare flavour-changing neutral current (FCNC) interactions of the top quark within the Standard Model Effective Field Theory (SMEFT). Matching a general top-FCNC parametrisation onto the SMEFT basis, we perform a global fit including low-energy flavour observables, electroweak precision data, Higgs measurements, collider limits on top-FCNC decays, and electric dipole moment constraints. Allowing for complex dipole operators, we derive stringent bounds on the real and imaginary parts of the top-FCNC couplings and, independently, obtain robust constraints on the corresponding SMEFT Wilson coefficients. We further provide predictions for rare top-FCNC branching ratios and CP asymmetries, and identify benchmark scenarios illustrating the complementary role of CP-violating observables in probing top-quark flavour dynamics.

77 pages, 21 Tables, 14 Figures. Current version accepted in JHEP; analysis updated with more inputs