The Effects of the Massless O(alpha_s^2), O(αα_s), O(α^2) QCD and QED Corrections and of the Massive Contributions to Gamma(H^0\rightarrow b\overline{b})

Abstract

We consider in detail various theoretical uncertainties of the perturbative predictions for the decay width of $H^0\rightarrow b\overline{b}$ process in the region $50\ GeV< M_H\leq 2M_W$. We calculate the order $O(α_s^2)$-contributions to the expression for $Γ_{Hb\overline{b}}$ through the pole quark mass and demonstrate that they are important for the elimination of the numerical difference between the corresponding expression and the one through the running $b$-quark mass. The order $O(αα_s)$ and $O(α^2)$ massless and order $O(m_b^2/M_H^2)$ massive corrections to $Γ_{Hb\overline{b}}$ are also calculated. The importance of the latter contributions for modeling of the threshold effects is demonstrated. The troubles with identifying of the 4 recent L3 events $e^+e^-\rightarrow l^+l^-γγ$ with the decay of a Standard Higgs boson are discussed.