Few-nucleon contribution to π-scattering on light nuclei

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