D→ππ decays with final state interactions

We study D→ππ decays with final state interactions considered in one-particle-exchange method. A clear physical picture for final state interactions based on quark and hadronic level diagrams is presented. A strong phase is introduced for hadronic effective couplings, which is crucial for explaining the experimental data of D+→π+π0, D0→π+π−, and D0→π0π0. Rescattering effects between different D decay channels are usually large. They are important for obtaining correct branching ratios for D→ππ decays in theoretical calculation.