Pion deuteron scattering length in effective field theory

The S wave pion deuteron scattering length is presented in an effective field theory approach of the two-nucleon system. We include pions as dynamical particles which allows us to calculate pion re-scattering contributions inside the deuteron. Two-nucleon two-pion contact interactions with unknown parameters not determined by chiral symmetry need to be introduced in order to renormalise the appearing divergences. By choosing their values accordingly we are able to accommodate the available experimental data. (author)