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We calculate the contributions to electroweak precision observables (EWPOs)due to a fourth generation of fermions with the most general (quark-)flavourstructure (but assuming Dirac neutrinos and a trivial flavour structure in thelepton sector). The new-physics contributions to the EWPOs are calculated atone-loop order using automated tools (FeynArts/FormCalc). No furtherapproximations are made in our calculation. We discuss the size of non-obliquecontributions arising from Z--quark--anti-quark vertex corrections and thedependence of the EWPOs on all CKM mixing angles involving the fourthgeneration. We find that the electroweak precision observables are sensitive totwo of the fourth-generation mixing angles and that the correspondingconstraints on these angles are competitive with those obtained from flavourphysics. For non-trivial 4x4 flavour structures, the non-oblique contributionslead to relative corrections of several permille and should be included in aglobal fit.

Electroweak Precision Observables within a Fourth Generation Model with General Flavour Structure