KS→γγ,KL→π0γγand unitarity

Agreement between the experimental value $\Gamma (K_S\to \gamma \gamma )$ and the number predicted via a one-loop chiral perturbation theory calculation has been cited as a success for the latter. On the other hand the one-loop prediction for the closely related process $K_L\to {\pi }^0\gamma \gamma$ has been found to be a factor 3 below the experimental value. Using the inputs of unitarity and dispersion relations, we demonstrate the importance of higher order loop effects to both of these processes.