Search for B^+ -> mu^+ nu and B^+ -> l^+ nu gamma decays

We have searched for the leptonic and radiative leptonic B decays, B^+ -> mu^+ nu, B^+ -> e^+ nu gamma and B^+ -> mu^+ nu gamma. Using a 140 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric e^+ e^- collider, we find no evidence for signals in any mode and set the following preliminary upper limits at 90% confidence level: BR(B^+ -> mu^+ nu) < 2.0 * 10^-6, BR(B^+ -> e^+ nu gamma) < 2.2 * 10^-5, and BR(B^+ -> mu^+ nu gamma) < 2.3 * 10^-5.