Electromagnetic pion and kaon form factors in light-cone resummed perturbative QCD

TL;DR

This paper investigates the electromagnetic form factors of pions and kaons using resummed perturbative QCD, highlighting the transition from soft to hard contributions across different energy scales and emphasizing the importance of including non-perturbative effects.

Contribution

The study introduces a modified k_T factorization scheme with transverse degrees of freedom to separately evaluate soft and hard contributions, ensuring no double counting and improving understanding of form factors.

Findings

Soft contributions dominate below 10-16 GeV^2.

Hard perturbative contributions become significant beyond 50-100 GeV^2.

Including soft effects is crucial for matching experimental data.

Abstract

We analyze the electromagnetic pion and kaon form factor by including radiative and higher-twist effects within the framework of resummed pQCD in the space-like region. We focus on the transition from the perturbative to non-perturbative behavior in the phenomenological intermediate energy regime. Using a modified k_T factorization scheme with transverse degrees of freedom, we evaluate the non-perturbative soft contributions as distinct from the hard contributions, ensuring no double counting via the Ward identity at Q^2=0. The soft contributions are obtained via local quark-hadron duality while the hard contributions rest on the well known collinear factorization theorem using model wave functions with modified Brodsky-Huang-Lepage type ansatz and distribution amplitudes derived from light-cone QCD sum rules. Our analysis shows that the perturbative hard part prevails for large Q^2 beyond 50-100 GeV^2, while for low and moderate momentum transfers below 10-16 GeV^2 the soft contributions dominate over the hard part. Thus, we demonstrate the importance of including the soft contributions for explaining the experimental form-factor data.