Long and short of nuclear effective field theory expansions - art. no. 064002

Nonperturbative effective field theory calculations for NN scattering seem to break down at rather low momenta. By examining several toy models, we cl arify how effective field theory expansions can in general be used to prope rly separate long- and short-range effects. We find that one-pion exchange has a large effect on the scattering phase shift near poles in the amplitud e, but otherwise can be treated perturbatively. Analysis of a toy model tha t reproduces S-1(0) NN scattering data rather well suggests that failures o f effective field theories for momenta above the pion mass can be due to sh ort-range physics rather than the treatment of pion exchange. We discuss th e implications this has for extending the applicability of effective field theories [S0556-2813(99)02011-7].