Pion and kaon form factors in the perturbative QCD approach

We present the most accurate calculation for the pion and kaon electromagnetic form factors in the framework of perturbative QCD, where the power corrections up to twist 4 of the meson distribution amplitudes and the next-to-leading-order QCD corrections up to subleading power are included. In order to guarantee the gauge invariance of the meson to vacuum matrix element, we take into account both assignments with the lowest Fock state and the high Fock state with an additional valence gluon. Our results confirm the power behavior of the twist expansion and show the chiral enhancement effect at subleading power in the PQCD approach. We also estimate the SU(3) asymmetry for the kaon and pion form factors and find that it is smaller than 30%.