Two-Loop $\mathcal{O}({\alpha }_s{G}_F{m}_t^2)$ Corrections to the Fermionic Decay Rates of the Standard-Model Higgs Boson

Abstract

Low- and intermediate mass Higgs bosons decay preferably into fermion pairs. The one-loop electroweak corrections to the respective decay rates are dominated by a flavour-independent term of $\mathcal{O}(G_F{m}_t^2)$. We calculate the two-loop gluon correction to this term. It turns out that this correction screens the leading high-$m_t$ behaviour of the one-loop result by roughly 10\%. We also present the two-loop QCD correction to the contribution induced by a pair of fourth-generation quarks with arbitrary masses. As expected, the inclusion of the QCD correction considerably reduces the renormalization-scheme dependence of the prediction.

Comments: 14 pages, latex, figures 2-5 appended, DESY 94-083