Twist-3 contribution to theγ*γ→ππamplitude in the Wandzura-Wilczek approximation

Zusammenfassung

We have calculated the Wandzura-Wilczek contribution to the twist-3 part of the gamma*gamma-->2 pi amplitude. It describes the interaction of the longitudinally polarized virtual photon with the real one, and it is suppressed by 1/Q where Q(2) is the virtuality of the gamma*, as compared to the twist-2 contribution. We have found that in the Wandzura-Wilczek approximation, factorization applies to the twist-3 amplitude.