O(alpha_s) corrections to longitudinal and transverse W-bosons in top quark decays

In this talk we consider the O(alpha_s) radiative corrections to the decay of an unpolarized top quark into a bottom quark and a W gauge boson where the helicities of the W are specified as transverse-plus, transverse-minus and longitudinal. The O(alpha_s) radiative corrections lower the normalized longitudinal rate Gamma_L/Gamma by 0.8%. We find that the normalized transverse-plus rate Gamma_+/Gamma, which vanishes at the Born term level for m_b->0, receives radiative correction contributions at the sub-percent level. Our results are discussed in the light of recent measurements of the helicity content of the W in top quark decays by the CDF Collaboration.