Weak radiative decays of Σ and Λ hyperons

Unitarity and dispersion theory are used to calculate the contribution of the π N intermediate state to the weak radiative decays of Σ and Λ hyperons. The contribution from the octet baryon poles is also calculated. The current × current form is assumed for the weak Hamiltonian so that the weak parity-violating two-body vertex vanishes in the limit of SU (3) symmetry and the parity-violating octet baryon pole terms are zero. Consequently the parity-violating weak radiative decay amplitude comes entirely from the π N intermediate state. Our main results are: (i) the contribution of the π N intermediate state is comparable to the contribution of the octet baryon pole terms and (ii) the correct sign and order of magnitude for the asymmetry parameter α and a branching ratio in moderate agreement with the recent experiment of Gershwin et al. are obtained for the decay Σ + → P γ .