Abstract
We show that most spectra in the semileptonic decay B -> X_u + l + nu, such as for example the distribution in the light-cone momentum p_+ = E_X - p_X recently considered, do not have the same long-distance structure of the photon spectrum in the radiative decay B -> X_s + gamma. On the contrary, the semileptonic distribution in the final hadron energy E_X is connected to the radiative spectrum via short-distance factors only. The E_X distribution also has a specific infrared structure known as the ``Sudakov shoulder''. We also discuss an explicit check of the resummation formula for the semileptonic decays, based on a recent second-order computation.
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