On convergence of the HFF expoansion for meson production in NN collisions

We consider the application of heavy fermion formalism based ChPT to meson production in nucleon-nucleon collisions. It is shown that to each lower chiral order irreducible diagram there corresponds an infinite sequence of loop diagrams which are of the same momentum power order. This destroys the one-to-one correspondence between the loop and small momentum expansion and thus rules out the application of any finite order HFF ChPT yo the NN-> NNpion reactions.