Abstract
We analytically compute the flavour singlet O(α s 2m b 2/m t 2) radiative corrections to the partial decay rate Γ(Z → b b) . These corrections arise from anomalous “double triangle” diagrams containing a single γ 5 matrix inside each of two closed fermion loops. They represent the next-to-leading term of the asymptotic expansion in the inverse large top mass. As a byproduct of the calculation we confirm the results of B. Kniehl and J.H. Kühn for the flavour singlet massless corrections [Phys. Lett. B 224 (1990) 229; Nucl. Phys. B 329 (1990) 547] as well as our previous O(α s 2m b 2/M Z 2) result [Phys. Lett. B 305 (1993) 285].
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