Unraveling the SMEFT Flavor Structure through cLFV Searches at Future Lepton Colliders

Future lepton colliders provide a uniquely clean and high-precision environment to probe charged lepton flavor violation (cLFV) at energy scales far beyond the reach of current experiments. Such facilities are particularly well suited to explore flavor-violating interactions with suppressed Standard Model backgrounds and well-controlled systematic uncertainties. In this work, we investigate a broad class of LFV operators in the Standard Model Effective Field Theory (SMEFT) framework across multiple collider configurations, focusing on multi-TeV electron–positron and muon machines envisioned for the next generation of high-energy lepton programs. Our analysis incorporates realistic assumptions about detector performance, particle identification, and beam polarization, enabling an accurate characterization of both the signal and the dominant Standard Model backgrounds. We explore the interplay between center-of-mass energy, integrated luminosity, and polarization configurations in enhancing LFV sensitivity, demonstrating how different collider setups provide complementary access to operator structures and chiral couplings. In addition to a traditional cut-based approach, we evaluate the impact of multivariate techniques and optimal observable strategies in extracting maximal information from kinematic distributions. Preliminary projections indicate that next-generation lepton colliders can improve sensitivity to LFV interactions relative to indirect limits derived from rare tauon decays. These results highlight the decisive role of future lepton collider programs in establishing a comprehensive global effort to uncover new sources of lepton flavor violation and in mapping the SMEFT flavor landscape with unprecedented precision.