The π-nucleus optical potential to O(p⁵) in Chiral Perturbation Theory

We describe the calculation of the π-nucleus optical potential to NLO in Chiral Perturbation Theory (ChPT) within a new formulation of the effective theory in the presence of a nuclear background, characterized by a static, non-uniform distribution of the baryon number, describing the finite nucleus. This formulation reduces to the conventional Inmedium ChPT in the case of a uniform distribution. In this way we are able to identify unambiguously the nuclear finite size effects and disentangle the S-, P - and D-wave contributions to the optical potential without invoking the local density approximation.