The decays KL,S→π0π0γγand KL→π0π0γin the effective chiral lagrangian approach

The decay amplitudes KL,S→π0π0γγ and KL→π0π0l+l- (l=e, μ) are calculated to lowest non-trivial order in chiral perturbation theory. The processes KLS→π0π0γγ are finite one-loop level and do not involve any unknown counterterm coupling constants. The one-loop amplitude for KL→π0π0l+l- is UV-divergent. It is renormalized by a local weak counterterm of order p4 appearing also in the decay amplitude for KS→π0l+l-. Using an SU(3) argument, this counterterm is related to the experimentally measured decay K+→π+l+l-. Detailed numerical results for the predicted decay rates and spectra are shown. (orig.)