Weak radiative hyperon decays in chiral perturbation theory

Abstract The parity-conserving a and parity-violating b amplitudes for weak radiative hyperon decay are studied using chiral perturbation theory. The imaginary parts of a and b are computed using unitarity. The real part of b is dominated by a one-loop infrared divergent graph which is computed. The real part of a has a large theoretical uncertainty and cannot be calculated reliably. Counterterms for the a and b amplitudes are classified using CPS symmetry. The experimental values for decay widths and asymmetries are consistent with theory, with the exception of the asymmetry parameter for the Σ + → p γ decay.