A new study explores the capability of the future electron-positron Future Circular Collider (FCC-ee) to detect flavor-changing neutral currents (FCNCs) in the third generation of fermions. These interactions, mediated by Z bosons and photons, are a fertile ground for the search for new physics, as the properties of the third generation, such as their significantly larger masses, are less precisely measured and could reveal deviations from the Standard Model (SM).

Researchers employed the Standard Model Effective Field Theory (SMEFT) formalism, using dipole and Higgs-current operators, to analyze transitions between the third and the first two generations of fermions. They used the optimal observable technique (OOT) to determine the optimal sensitivity of the FCC-ee at different center-of-mass energies. Additionally, they complemented this analysis with existing constraints from low-energy flavor-violating observables and heavy fermion decay channels.

The study also revealed characteristic interference patterns among the dipole contributions, which vary depending on the underlying flavor transition and exhibit distinct behavior between the Z pole and higher-energy FCC-ee stages. Projections indicate improved sensitivity for several of these interactions compared to current limits, and comparable sensitivity for others. This highlights the importance of a systematic assessment across the different FCC-ee energy stages to obtain a comprehensive picture of its potential in exploring flavor-violating phenomena and its complementarity with low-energy flavor experiments.