Revisiting Weak Radiative Decays of Hyperons

Abstract

Triggered by experimentally driven renewed interest in hyperon properties we address the subject of weak radiative hyperon decays (WRHD). We start with the issue of Hara's theorem and briefly discuss the question of its possible evasion. Then, we give a short review of the story of vector-meson-dominance (VMD) approach to WRHD. We stress the shift from the Hara's-theorem-violating to Hara's-theorem-satisfying version of the VMD approach that did occur over time. Finally, spurred by a recent theoretical paper, we discuss the pole model description of WRHD, putting special attention to the issue of the contributions from the intermediate $\Lambda(1405)$ state. We point out that the measurement of the $\Lambda \to n \gamma$ decay asymmetry could resolve the encountered ambiguities and definitely answer the question of whether Hara's theorem is violated or not.