O(ααsln mt2) non-universal corrections to the decay rate Γ(Z → bb)

The partial decay rate Γ(Z → bb) is significantly influenced by the mass of the top quark due to electroweak radiative corrections. The leading ∼ mt2 and the next-to-leading contribution ∼ ln mt2 are known to be numerically of similar size. In this work we calculate the QCD corrections to the logarithmic correction using the heavy top mass expansion. TheO(ααsln mt2) corrections are of the same order as the QCD corrections to the quadratic top mass term, but of different sign.