Revisiting Weak Radiative Decays of Hyperons

TL;DR

This paper reviews weak radiative hyperon decays, discussing theoretical approaches like Hara's theorem, vector-meson dominance, and pole models, emphasizing the importance of decay asymmetry measurements to resolve existing ambiguities.

Contribution

It provides a comprehensive review of theoretical models for WRHD, highlighting the evolution of the VMD approach and proposing the decay asymmetry measurement as a key to resolving Hara's theorem violations.

Findings

Shift from Hara's-theorem-violating to satisfying VMD models

Pole model analysis emphasizes the role of $ extstyle ext{Λ}(1405)$

Decay asymmetry measurements could clarify Hara's theorem status

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.