[en] Electroweak radiative one-loop corrections to Higgs boson pair production in t bar t fusion processes are calculated in the two-Higgs-doublet extension of the standard model. The numerical size of the nonstandard corrections is discussed for the process t bar t→H₀H₀. The relative difference between the predictions of the two-Higgs-doublet model and the minimal standard model for a light scalar M_H1 and heavy M_H2 and M_Φ easily exceeds -10% in the forward and backward directions. In particular the angular-dependence corrections owing to the nonstandard Higgs bosons get larger where the box and cubic Higgs boson vertex corrections constitute the dominant part of the radiative corrections. copyright 1996 The American Physical Society

[en] The weak corrections at the one-loop level to the process H₀→t bar t in the two-Higgs-doublet extension of the standard model are calculated. The correction from the additional Higgs sector may become negative and cancel the correction part from the standard model. With the heavy H₀ boson, the additional Higgs sector corrections may easily exceed -20%, owing to the relatively light H₁ mass and rather heavy H₂, Φ masses. That makes the total weak quantum corrections only a few percent in the two-Higgs-doublet model. The calculation shows the general two-Higgs-doubet model has flexibility in regulating loop corrections

[en] In the two-Higgs-doublet model the complete nonstandard Higgs boson helicity amplitudes for the Higgs boson pair production process γγ→H₀H₀ is calculated and explicit formulas for nonstandard Higgs boson contributions to the helicity amplitudes are given. It is shown that the cross section is in the range of 0.03 endash 30 pb at √s=1 TeV, for Higgs boson masses of 350< M_H0<490 GeV in monochromatic γγ collisions. The angular distribution for Higgs pair production is strongly peaked in the forward and backward directions. In particular the angular dependence for Higgs pair production is due to the nonstandard Higgs boson getting larger where the box diagrams constitute the dominant part of the differential cross section. For studying heavy Higgs pair production the use of circularly polarized photon beams with equal helicities is advantageous. copyright 1996 The American Physical Society

[en] The electroweak corrections at one-loop level to the process H→t bar t are calculated, incorporating the top mass value announced recently by CDF. For M_H<1 TeV where a perturbative calculation is valid, the corrections themselves would gain a few to 20% increment in the decay width as the Higgs-boson mass M_H is increasing within the region, but they are in opposite direction to the QCD ones. If the electroweak and QCD corrections are considered together, the resultant decay width of the mode yields a reduction about a few percent of the tree level one

[en] Electroweak radiative one-loop corrections to the process γγ→W⁺W^- with photon and W-boson polarizations are calculated within the two-Higgs-doublet model extension of the standard model, and the relevant analytical results for the nonstandard Higgs bosons contributions to the helicity amplitudes are given. The relative difference between the predictions of the two-Higgs-doublet model and minimal standard model for a light salar M_H1 and heavy M_H2 and M_Φ easily exceed ±20% for W_TW_T pair production in the central angular region at high energy, and even larger for W_LW_L pair production. The angular dependence corrections owing to the nonstandard Higgs boson get larger, where box diagrams constitute the dominant part of the radiative corrections. copyright 1997 The American Physical Society