Exclusive meson pair production in γγ scattering at small momentum transfer

We study the exclusive production of ππ and ρπ in hard γγ scattering in the forward kinematical region where the virtuality of one photon provides us with a hard scale in the process. The newly introduced concept of Transition Distribution Amplitudes (TDA) is used to perform a QCD calculation of these reactions thanks to two simple models for TDAs. Cross sections for ρπ and ππ production are evaluated and compared to the possible background from the Bremsstrahlung process. This picture may be tested at intense electron-positron colliders such as CLEO and B factories. The cross section eγ → e′π0π0 is finally shown to provide a possible determination of the π axial form factor, F π 0 A , at small t, which seems not to be measurable elsewhere.