Two-body decays of charm mesons and the role of exotic mesons

Two-body decays of charm mesons (except for decays into the final states involving $\eta$ or ${\eta }^{\prime }$) are studied from a perspective in which dynamical contributions of hadrons are explicitly taken into account. All the observed values of branching ratios for the two-body decays of charm mesons are reproduced well. In particular, a solution to the well-known puzzle, $\frac{\Gamma (D^0\to K^{+}{K}^{-})}{\Gamma (D^0\to {\pi }^{+}{\pi }^{-})}\simeq 2-3$, is presented. Contributions of exotic $\mathrm{}\left(\mathrm{QQ}\right)\left(\overline{Q}\overline{Q}\right)$ mesons can explain the large violation of the charm counterpart of the $\left|\Delta I\right|=\frac{1}{2}$ rule in consistency with the small violation of the $\left|\Delta I\right|=\frac{1}{2}$ rule in the $K\to \pi \pi$ decays.