IsD0→φK¯0really a clear signal for the annihilation diagram?

It is shown that rescattering effects required by unitarity can produce the reaction $D^0$→φK${¯}^0$, even when the ‘‘W-exchange’’ or ‘‘annihilation’’ diagram is not present. This is addressed both in a general context and a specific model. In the latter, it is the mode $D^0$→$K^{\mathrm{*}}$η which plays the major role in generating the φK final state, as the $K^{\mathrm{*}}$η state is produced using the uū component of the η, and scatters, $K^{\mathrm{*}}$η→Kφ by quark exchange, utilizing the ss¯ component of the η. .AE