Removing pions from two-nucleon effective field theory

Two-nucleon effective field theory (EFT) beyond momenta of order the pion m ass is studied for both cutoff regularization and dimensional regularizatio n with power divergence subtraction (PDS). Models with two mass scales illu strate how effects of long-distance pion physics must be removed from the c oefficients that encode short-distance physics. The modified effective rang e expansion shows that treating pions perturbatively, as in the PDS power c ounting, limits the radius of convergence of the EFT. Predictions from both regularization schemes with one-pion contributions are compared to data. T he breakdown of the effective field theory occurs for momenta of order 300 MeV, even using the modified effective range expansion. This behavior is sh own to be consistent with that expected from two-pion contributions. (C) 19 99 Elsevier Science B.V.