We analyze the Chiral Perturbation Theory predictions for γγ->π⁰π⁰ to two loops. The amplitude to this order depends on three new counterterms which can be estimated using resonance excange. The low-energy cross section is in good agreement with the present data and with calculations based on dispersion relations. We predict the Compton cross section and the neutral pion polarizabilities to the two-loop order. The unitarization of the one-loop cross section is also discussed.
Bellucci S. (Mon,) studied this question.
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