Anatomy of flavour-changing Z couplings in models with partial compositeness

摘要

In models with partially composite quarks, the couplings of quarks to the Zboson generically receive non-universal corrections that are not onlyconstrained by electroweak precision tests but also lead to flavour-changingneutral currents at tree level. The impact of these flavour-changing couplingson rare K and B decays is studied in two-site models for three scenarios: ananarchic strong sector with two different choices of fermion representationsboth leading to a custodial protection of the Z->bb coupling, and for a strongsector invariant under a U(2)^3 flavour symmetry. In the complete numericalanalysis, all relevant constraints from Delta(F)=2 processes are taken intoaccount. In all scenarios, visible effects in rare K and B decays like K->pi nuanti-nu, B(s)->mu+mu- and B->K*mu+mu- are possible that can be scrutinizedexperimentally in the near future. Characteristic correlations betweenobservables allow to distinguish the different cases. To sample the largeparameter space of the anarchic models, a new method is presented that allowslarger statistics than conventional approaches.