We present a first, consistent combination of measurements from top-quark and B physics to constrain topquark properties within the Standard Model Effective Field Theory (SMEFT). We demonstrate the feasibility and benefits of this approach and detail the ingredients required for a proper combination of observables from different energy scales. Specifically, we employ measurements of the ttγ cross section together with measurements of theB → X s γ branching fraction to test the Standard Model and look for new physics contributions to the couplings of the top quark to the gauge bosons within SMEFT. We perform fits of three Wilson coefficients of dimension-six operators considering only the individual observables as well as their combination to demonstrate how the complementarity between top-quark and B physics observables allows to resolve ambiguities and significantly improves the constraints on the Wilson coefficients. No significant deviation from the Standard Model is found with present data.

We investigate collider signatures of standard model extensions featuring vector-like leptons and a flavorful scalar sector. Such a framework arises naturally within asymptotically safe model building, which tames the UV behavior of the standard model towards the Planck scale and beyond. We focus on values of Yukawa couplings and masses which allow to explain the present data on the muon and electron anomalous magnetic moments. Using a CMS search based on $$77.4 \, \text {fb}^{-1}$$ 77.4 fb - 1 at the $$\sqrt{s}=13$$ s = 13  TeV LHC we find that flavorful vector-like leptons are excluded for masses below around 300 GeV if they are singlets under $$SU(2)_L$$ S U ( 2 ) L , and around 800 GeV if they are doublets. Exploiting the flavor-violating-like decays of the scalars, we design novel null test observables based on opposite sign opposite flavor invariant masses. These multi-lepton distributions allow to signal new physics and to extract mass hierarchies in reach of near-future searches at the LHC and the HL-LHC.

We perform global fits within Standard Model Effective Field Theory (SMEFT) combining top-quark pair production processes and decay with b → s flavor changing neutral current transitions and Z → $$ b\overline{b} $$ b b ¯ in three stages: using existing data from the LHC and B-factories, using projections for the HL-LHC and Belle II, and studying the additional new physics impact from a future lepton collider. The latter is ideally suited to directly probe ℓ+ℓ− → $$ t\overline{t} $$ t t ¯ transitions. We observe powerful synergies in combining both top and beauty observables as flat directions are removed and more operators can be probed. We find that a future lepton collider significantly enhances this interplay and qualitatively improves global SMEFT fits.

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