Pion Deuteron Scattering and Chiral Expansions

We discuss convergence issues as well as short distance constraints on the deuteron wave functions based on chiral perturbation theory relevant to pion deuteron scattering. Non-analytical terms arise in the multiple scattering series for the pion-deuteron scattering length limiting the accuracy of the calculations. This result resembles similar findings in the structure of the NN interaction. The effects are found not to be numerically large. The iso-scalar $\pi N$ scattering length from the iso-vector one and the $\pi d$ scattering length yields values compatible with the experimental number and with much smaller errors.