K_S\rightarrow γγ, K_L\rightarrowπ^0γγ$ and Unitarity

Abstract

Agreement between the experimental value $Γ(K_S\rightarrow γγ)$ 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 $K_L\rightarrow π^0γγ$ has been found to be a factor three 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.