Power corrections to B\to X_u l \nu (X_s\gamma) decay spectra in the "shape-function" region

Using soft-collinear effective theory (SCET), we examine the 1/m_b corrections to the factorization formulas for inclusive semi-leptonic B decays in the endpoint region, where the hadronic final state consists of a single jet. At tree level, we find a new contribution from four-quark operators that was previously assumed absent. Beyond tree level many sub-leading shape-functions are needed to correctly describe the decay process.