Leveraging recent advancements in machine learning-based flavor tagging, we develop an optimal analysis for measuring the hadronic cross-section ratios $R_b$, $R_c$, and $R_s$ at the FCC-ee during its $WW$, $Zh$, and $t\bar{t}$ runs. Our results indicate up to a two-order-of-magnitude improvement in precision, providing an unprecedented test of the SM. Using these observables, along with $R_\ell$ and $R_t$, we project sensitivity to flavor non-universal four-fermion (4F) interactions within the SMEFT, contributing both at the tree level and through the renormalization group (RG). We highlight a subtle complementarity with RG-induced effects at the FCC-ee's $Z$-pole. Our analysis demonstrates significant improvements over the current LEP-II and LHC bounds in probing flavor-conserving 4F operators involving heavy quark flavors and all lepton flavors. As an application, we explore simplified models addressing current $B$-meson anomalies, demonstrating that FCC-ee can effectively probe the relevant parameter space. Finally, we design optimized search strategies for quark flavor-violating 4F interactions.

We propose a unique topological portal between quantum chromodynamics (QCD) and a dark sector characterized by a global symmetry breaking, which connects three QCD to two dark pions. When gauged, it serves as the leading portal between the two sectors, providing an elegant, self-consistent scenario of light thermal inelastic dark matter. The inherent antisymmetrization leads to diminished annihilations at later times and suppressed direct detection. However, novel collider signatures offer tremendous prospects for discovery at Belle II.

The stability of the electroweak scale, challenged by the absence of deviations in flavor physics, prompts the consideration of SMEFT scenarios governed by approximate SM flavor symmetries. This study examines microscopic theories that match onto a set of $U(3)^5$-symmetric dimension-6 operators. Renormalization group mixing from the ultraviolet to the electroweak scale yields significant phenomenological constraints, particularly pronounced for UV-motivated directions. To demonstrate this, we explore a complete suite of tree-level models featuring new spin-0, 1/2, and 1 fields, categorized by their irreducible representations under the flavor group. We find that for the leading directions, corresponding to a single-mediator dominance, RG mixing effects occasionally serve as the primary indirect probe.

We posit that the distinct patterns observed in fermion masses and mixings are due to a minimally broken U(2)_{q+e} flavor symmetry acting on left-handed quarks and right-handed charged leptons, giving rise to an accidental U(2)^{5} symmetry at the renormalizable level without imposing selection rules on the Weinberg operator. We show that the symmetry can be consistently gauged by explicit examples and comment on realizations in SU(5) unification. Via a model-independent analysis of a standard model viewed as an effective field theory, we find that selection rules due to U(2)_{q+e} enhance the importance of charged lepton flavor violation as a probe, where significant experimental progress is expected in the near future.