Few-nucleon contribution to π-scattering on light nuclei

We present our new results of the few-nucleon contributions to π-2H, π-3He and π-4He scattering lengths. To calculate these within the framework of Chiral Perturbation Theory we used a Monte-Carlo algorithm, which is brie y introduced. The size of the two-, three- and four-nucleon corrections in view of the expectations from two di erent power counting schemes is discussed. Based on our results, we estimate short range contributions, which limit the accuracy of the πN scattering lengths extracted from few-nucleon data. Additionally, we study how the π-4He system constrains the determination of the isoscalar s-wave scattering length a(+) and its isovector counter part a( ) .