Unitarity and vector meson contributions to K+ → π+γγ

We compute the one-loop unitarity corrections O(p6) from K+ → π+π+π− to K+ → π+γγ and we find that they are relevant, increasing the leading order prediction for the width in a 30–40%. The contributions of local O(p6) amplitudes, generated by vector meson exchange, are discussed in several models and we conclude that the vector resonance contribution should be negligible compared to the unitarity corrections.