Effective Theory Description of Weak Annihilation in B-> Xu l nu Decays
  The semileptonic B-> Xu l nu decays allow a pretty clean determination of the CKM matrix element |Vub|. Nevertheless, the presence of weak-annihilation effects near the end-point of the q2 spectrum introduces uncertainties in the inclusive calculation, requiring the use of non-perturbative techniques like heavy meson chiral perturbation theory and large NC limit. 
J.J. Sanz-Cillero