Abstract A scalar singlet particle, named U, is coupled to the Higgs sector of the standard model for the purpose of parametrizing the large Higgs mass behaviour of the theory. The radiative corrections to the low-energy parameters (ϱ parameter, W mass shift) are computed at one- and two-loop levels. The new contributions demonstrate the arbitrariness of the heavy-Higgs theory, i.e., the dependence on the way of taking the large-Higgs-mass limit, but they fail to restore its uniqueness. The U particle effects at high energies are examined in accordance with partial wave analysis methods developed in the study of ππ scattering. The corrections to the β parameter are derived from the longitudinal vector boson scattering amplitude calculated below the 1 TeV threshold. Assuming a small, of the order of 10%, difference between the masses of the scalars, we find a small but positive enhancement to the standard model contributions. The overall result indicates that no resonance will appear in the isospin I=1 channel at any energy above the threshold.