Comment on evidence for new interference phenomena in the decay D+→K−π+μ+ν

The experimental determination of low energy πK scattering phase shifts would assist in determining scattering lengths as well as low energy constants of chiral perturbation theory for which sum rules have been constructed. The FOCUS Collaboration has presented evidence for interference phenomena from their analysis of Dl4 decays based on decay amplitudes suitable for a cascade decay D→K∗→Kπ. We point out that if the well-known full five body kinematics are taken into account, πK scattering phases may be extracted. We also point out that other distributions considered in the context of Kl4 decays can be applied to charm meson decays to provide constraints on violation of |ΔI|=1/2 rule and T-violation.