Contributions to the width difference in the neutral $D$ system from hadronic decays

Recent studies of several multi-body $D^0$ meson decays have revealed that the final states are dominantly $CP$-even. However, the small value of the width difference between the two physical eigenstates of the $D^0$-$\overline{D}{}^0$ system indicates that the total widths of decays to $CP$-even and $CP$-odd final states should be the same to within about a percent. The known contributions to the width difference from hadronic $D^0$ decays are discussed, and it is shown that an apparent excess of quasi-$CP$-even modes is balanced, within current uncertainty, by interference effects in quasi-flavour-specific decays. Decay modes which may significantly affect the picture with improved measurements are considered.