Violation of the Vacuum Symmetry, Decay Constants and the Mixing of "11 " Mesons*>

Properties of pseudoscalar mesons in the four-flavour QCD model are studied in detail. Their masses, mixings and decay constants are correlated, more or less strongly, to the structure of symmetry breaking of the vacuum. Through an extensive numerical analysis, it is shown, among other things, that the vacuum obeys an approximate SU (3) XU (1) symmetry rather than SU(4), the violation of the latter of which is reflected in the magnitudes of decay constants of charmed mesons. § 1. Introduction an