Complete QCD Corrections of Order O(α_s³) to the Hadronic Higgs Decay

We consider the decay of an intermediate mass Higgs boson into hadrons up to order O(\alpha_s^3). The results from the diagrams containing only light degrees of freedom were recently computed in a previous work by K.G. Ch. (Phys. Lett. B 390 (1997) 309). In this letter the remaining contributions involving the top quark are evaluated analytically using an effective field theory approach. Coupled with the previous result the present calculation determines the complete next-next-to-leading order correction to the hadronic decay rate of an intermediate mass Higgs boson.