Light Meson Decay Constants
  We estimate the decay constants $f_\pi$ and $f_K$ of the light mesons within a relativistic quantum-field model of interacting quarks and gluons confined analytically. The necessary physical parameters, the quark masses $m_u$ and $m_s$, the coupling constant $\alpha_s$ and the confinement scale $\Lambda$ have been obtained from our previous investigation on the meson ground states, orbital and radial excitations by using the ladder Bethe-Salpeter equation. Our approach provides a solid framework to compute the meson spectra, the lowest glueball state and decay constants of pseudoscalar mesons (as well as other physical observables) nonperturbatively from the basic principles of QCD and QFT. 
G. Ganbold