Meson pair production in two-photon processes

We investigate the amplitudes $\text{γγ → ππ}\text{and}\text{ππ →}\text{K}\text{K}$ by performing a coupled-channel calculation of the final-state interactions in these processes which play a crucial role in reactions like $\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{ππ (}\text{or K}\text{K}\text{)}$. Among our most interesting results we find that the S¹ effect shows up very clearly in these reactions, and that there is an important enhancement in the I = 0 s-wave amplitudes in a large energy range, from threshold to 1.5 GeV, which leads to the prediction of abundant π⁰π⁰ production in such reactions. We also make some comments on the general treatment of final-state interactions.