Abstract
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 behaviour of the twist expansion and show the chiral enhancement effect at subleading power in the PQCD approach. We also estimate the $\mathrm{SU(3)}$ asymmetry for the kaon and pion form factors and find that it is smaller than $30 \%$.
Highlights
The quantum chromodynamics (QCD) has two fundamental properties: the quark confinement in the low energy region and the asymptotic freedom in the high energy region
We study the pion and kaon electromagnetic form factors with the inclusion of the high power contributions up to twist 4 of the meson distribution amplitudes (DAs); the perturbative QCD (PQCD) calculation confirms the convergence behavior of the twist expansion, which shows that the contribution from the three-parton Fock state is at least 1 order of magnitude smaller than that from the lowest Fock state
The chiral enhancement of the subleading power contribution depends strongly on the corresponding DAs, and this effect is quite obvious in our choice of the conformal expansion of twist-3 DAs
Summary
The quantum chromodynamics (QCD) has two fundamental properties: the quark confinement in the low energy region and the asymptotic freedom in the high energy region. In the perturbative QCD (PQCD) approach, it is described by a hard scattering amplitude [7,15] and can be calculated perturbatively. In this paper we calculate the higher power corrections to pion and kaon form factors up to twist 4 of the meson distribution amplitudes (DAs), with the aim to check the power expansion behavior from one side, and from the other side to improve the theoretical accuracy in the framework of PQCD approach.
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