The strong coupling constant $g_{D^* D \pi}$ and final-state interactions

In this article, we study the contribution from the final-state interactions to the strong coupling constant $g_{D^* D \pi}$. We take an assumption that the momentum transfers in the strong decay $D^{*+} \to D^0 \pi^+$ be large to validate the operator product expansion in the light-cone QCD sum rules. At large momentum transfers, the final-state interactions play an important role, and we should take them into account.