Two-loop virtual top-quark effect on Higgs-boson decay to bottom quarks

In most of the mass range encompassed by the limits from the direct search and the electroweak precision tests, the Higgs boson of the standard model preferably decays to bottom quarks. We present, in analytic form, the dominant two-loop electroweak correction, of O(G_F^2 m_t^4), to the partial width of this decay. It amplifies the familiar enhancement due to the O(G_F m_t^2) one-loop correction by about +16% and thus more than compensates the screening by about -8% through strong-interaction effects of order O(alpha_s G_F m_t^2).