Analysis of O(p2) corrections to 〈ππ|Q7,8|K〉

The one-loop corrections to K→π and K→2π matrix elements of the electroweak penguin operator are calculated. General next-to-leading order relations between the K→π and K→2π amplitudes are obtained. The fractional shift Δ2=0.27±0.27 is found for the O(p2) corrections to a recent chiral determination of 〈(ππ)I=2|Q7,8|K0〉. We explain why the sign for Δ2 is opposite to that expected from unitarization approaches based on the Omnès equation. We perform a background-field, heat-kernel determination of the divergent one-loop amplitudes for a general class of (V−A)×(V+A) operators.