2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/40249We discuss a little-studied class of weak decay modes sensitive to only one quark topology at leading order in G_F: M --> m gamma, where M,m are mesons with completely distinct flavor quantum numbers. Specifically, they proceed via the annihilation of the valence quarks through a W and the emission of a single hard photon, and thus provide a clear separation between CKM and strong interaction physics. We survey relevant calculations performed to date, discuss experimental discovery potential, and indicate interesting future directions.10 pages LaTeX, includes macros file and 9 .eps figures. Invited talk at RADCOR 2000 (5th Int. Symp. on Radiative Corrections), Carmel, CA, Sept. 2000High Energy Physics - Phenomenologytext