Pion and Kaon Masses and Pion Form Factors from Dynamical   Chiral-Symmetry Breaking with Light Constituent Quarks
  Light constituent quark masses and the corresponding dynamical quark masses are determined by data, the quark-level linear sigma model, and infrared QCD. This allows to define effective nonstrange and strange current quark masses, which reproduce the experimental pion and kaon masses very accurately, by simple additivity. In contrast, the usual nonstrange and strange current quarks employed by the Particle Data Group and Chiral Perturbation Theory do not allow a straightforward quantitative explanation of the pion and kaon masses. 
Michael D. Scadron, Frieder Kleefeld, George Rupp