Weak radiative hyperon decay

A hyperon decay that changes quark flavour while emitting a photon. An example is ${\Xi }^0\to \Lambda \gamma$, which changes strangeness and cannot be purely electromagnetic. Its amplitude can contain short-distance loops and long-distance hadronic contributions. photon attachments to a weak quark-exchange graph must be completed consistently with electromagnetic gauge invariance. A quark topology identifies allowed flavour flow but does not by itself calculate a reliable hadronic rate.