2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/214901It has recently been pointed out that a new class of subleading shape functions involving B-meson matrix elements of non-local four-quark operators contributes at order Lambda_{QCD}/m_b to B->X_u+l+nu decay distributions in the endpoint region. The corresponding functions f_u(omega) and f_v(omega) are estimated using the vacuum-insertion approximation. A numerical analysis of various B->X_u+l+nu decay spectra suggests that these power corrections are very small, below present theoretical uncertainties due to other subleading shape-function contributions.8 pages, 2 figures; minor revisions and figure added; version to appear in Eur. Phys. J. CHigh Energy Physics - Phenomenologytext