The top decay t →bW in the two Higgs doublet model

Electroweak radiative one-loop corrections to the top decay with Γ(t→bW+) are calculated in the two Higgs doublet extension of the Standard Model. Whereas in the Minimal Standard Model the corrections are always below 2% and positive if the lowest-order width is parameterized by GF and MW they may become negative and much larger in the general Two Higgs Doublet Model. In particular for a light scalar Higgs boson and enhanced top quark Yukawa couplings (corresponding to a large top mass) the corrections owing to the additional Higgs bosons easily exceed -10%. For supersymmetric values of the parameters, however, the non-standard corrections hardly reach 1%. (orig.)