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

Abstract

We analyze the electromagnetic pion and kaon form factor by including radiative and higher-twist effects within the framework of resummed perturbative QCD in the spacelike region. We focus on the transition from the perturbative to nonperturbative behavior in the phenomenological intermediate-energy regime. Using a modified ``${k}_{T}$'' factorization scheme with transverse degrees of freedom, we evaluate the nonperturbative 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 $50--100\text{ }\text{ }{\mathrm{GeV}}^{2}$, while for low and moderate momentum transfers below $10--16\text{ }\text{ }{\mathrm{GeV}}^{2}$, 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.