Flavor dependence of the pion and kaon form factors and parton distribution functions

The separate quark flavor contributions to the pion and kaon valence quark distribution functions are studied, along with the corresponding electromagnetic form factors in the space-like region. The calculations are made using the solution of the Bethe-Salpeter equation for the model of Nambu and Jona-Lasinio with proper-time regularization. Both the pion and kaon form factors and the valence quark distribution functions reproduce many features of the available empirical data. The larger mass of the strange quark naturally explains the empirical fact that the ratio u_K⁺(x)/u_π⁺(x) drops below unity at large x, with a value of approximately Mᵤ²/Mₛ² as x→1. With regard to the elastic form factors we report a large flavor dependence, with the u-quark contribution to the kaon form factor being an order of magnitude smaller than that of the s-quark at large Q², which may be a sensitive measure of confinement effects in QCD. Surprisingly though, the total K⁺ and π⁺ form factors differ by only 10%. In general we find that flavor breaking effects are typically around 20%.