η → π0γγ to O(p6) in chiral perturbation theory Original Research Article

The decay η → π0γγis discussed in the framework of SU(3) chiral perturbation theory. The process is dominated by the O(p6) in the momentum expansion where tree-level amplitudes from the effective Lagrangian G6 enter together with one-loop contributions from λ4 and twoloop contributions from L6. We estimate the six independent L6 coupling constants by resonance saturation consistent with the pion production process γγ → π0π0 and calculate the pion-loop part of the one- and two-loop amplitude. Predictions for the total rate and spectrum of η → π0γγ are given together with a discussion of the uncertainties involved.