Few-Body Descriptions of the piNN System in Three and Four Dimensions

We summarise the recent theoretical progress in few-body descriptions of the piNN system. Previous descriptions, both three- and four-dimensional, are shown to possess serious theoretical inconsistencies. We illustrate how three-dimensional approaches suffer from renormalisation problems, and how four-dimensional descriptions contain both overcounting and undercounting of diagrams. We then show how such theoretical problems have been recently overcome, leading to new practical few-body equations for the piNN system.