Heavy-to-Light-Quark Decays with Two-Loop Accuracy

We present a determination of a new class of three-loop Feynman diagrams describing heavy-to-light transitions. We apply it to find the O(αₛ²) corrections to the top quark decay t→bW and to the distribution of lepton invariant mass in the semileptonic b quark decay b→ulν. We also confirm the previously determined total rate of that process as well as the O(α²) corrections to the muon lifetime.