Charged-Higgs-boson search via heavy-top-quark decay at Fermilab Tevatron collider energy

Assuming a top-quark mass of about 150 GeV we analyze the prospects for a charged-Higgs-boson search in top-quark decay at the Fermilab Tevatron upgrade. Universality predicts the relative size of the top decay signal via $W$ boson in different decay channels, and an observable excess over this prediction can be used as a signature for charged-Higgs-boson production. In the charged-Higgs-boson-fermion coupling scheme suggested by minimal supersymmetry and ${\mathrm{E}}_6$ string-inspired models one expects to see an observable signal up to a charged-Higgs-boson mass of 100 GeV throughout the allowed range of the coupling parameter $tan\beta$. The absence of such a signal would give an unambiguous charged-Higgs-boson mass limit of 100 GeV. This is not possible however in the alternative coupling schemes of two-Higgs-doublet models.