Mesons in the low-energy limit of QCDh

Quark-antiquark bound states are described within the Bethe-Salpeter approach for a class of quark models with instantaneous 4-quark interaction. Thereby decompositions of the Bethe-Salpeter vertex and wave functions according to their Lorentz structures and the particle content are used. Normalization conditions for the bound state functions are given. As an application of the general scheme, the mass spectrum of low-lying mesons without expanding in energy is determined. This calculation is performed for a special Nambu-Jona-Lasinio model which follows from the so-called QCD for hadrons, QCDh, by a localization of the potential. Furthermore the pion and kaon decay constants are determined. Good agreement with the experimental data is received. 12 refs.; 1 tab