Higgs-Boson Production and Decay Close to Thresholds

At one loop in the conventional on-mass-shell renormalization scheme, the production and decay rates of the Higgs boson H exhibit singularities proportional to (2 M_V - M)^{-1/2} as the Higgs-boson mass M approaches from below the pair-production threshold of a vector boson V with mass M_V. This problem is of phenomenological interest because the values 2 M_W and 2 M_Z, corresponding to the W- and Z-boson thresholds, lie within the M range presently favoured by electroweak precision data. We demonstrate how these threshold singularities are eliminated when the definitions of mass and total decay width of the Higgs boson are based on the complex-valued pole of its propagator. We illustrate the phenomenological implications of this modification for the partial width of the H -> W^+ W^- decay.