We use once-subtracted dispersion relations and current commutation relations to obtain the physical, hard-pion $\eta \to {\pi }^{+}{\pi }^{-}\gamma$ decay width in terms of the $\rho \to \eta \gamma$ decay width, thus making a prediction for the latter.

• Received 24 March 1969

DOI:https://doi.org/10.1103/PhysRev.185.2024