Vector-meson contributions to the processes γγ→π0π0,π+π-, KL→π0γγ, and K+→π+γγ

We implement standard chiral perturbation theory to O(p4) by adding vector mesons. We show that it leads to a good agreement of the prediction for σ(γγ→π0π0) with experiments and the vector mesons unitarize the chiral amplitude in an effective way. We also consider KL→π0γγ, including the effect of vector mesons, and obtain a very distinct spectrum for two photons. Also, their effects on γγ→π+π- and K+→π+γγ are briefly discussed