ETA-]PI(0)GAMMA-GAMMA TO O(P(6)) IN CHIRAL PERTURBATION-THEORY

The decay eta --> pi(0) gamma gamma is discussed in the framework of S U(3) chiral perturbation theory. The process is dominated by the O(p(6 )) in the momentum expansion where tree-level amplitudes from the effe ctive Lagrangian L(6) enter together with one-loop contributions from L(4) and two-loop contributions from L(2). We estimate the six indepen dent L(6) coupling constants by resonance saturation consistent with t he pion production process gamma gamma --> pi(0) pi(0) and calculate t he pion-loop part of the one- and two-loop amplitude. Predictions for the total rate and spectrum of eta --> pi(0) gamma gamma are given tog ether with a discussion of the uncertainties involved.