Breakdown of nonet symmetry in Cabibbo-allowed decays of charmed mesons into two pseudoscalars

We assume the flavor-symmetry properties predicted by the standard model for the decays of charmed mesons into two pseudoscalar mesons and test the additional hypothesis of nonet symmetry. From the measured branching ratios for $D^{+}$ and $D^0$, we show that nonet symmetry must be badly broken for the pseudoscalar nonet. Because the branching ratios for the $D_s$ meson are not well known at present, we cannot determine whether one of the SU(3) representations 6* and 15 dominates the effective interaction. There are some indications that both are equally important.