Probing the convergence of perturbative series in baryon chiral   perturbation theory
  Using the examples of pion-nucleon scattering and the nucleon mass we analyze the convergence of perturbative series in the framework of baryon chiral perturbation theory. For both cases we sum up sets of an infinite number of diagrams by solving equations exactly and compare the solutions with the perturbative contributions. 
D. Djukanovic, J.Gegelia, S. Scherer