Charge independence breaking and charge symmetry breaking in the nucleon-nucleon interaction from effective field theory

We discuss charge symmetry and charge independence breaking in an effective field theory approach for few-nucleon systems. We systematically introduce strong isospin-violating and electromagnetic operators in the theory. The charge dependence observed in the nucleon-nucleon scattering lengths is due to one-pion exchange and one electromagnetic four-nucleon contact term. Th is gives a parameter free expression for the charge dependence of the corre sponding effective ranges, which is in agreement with the rather small and uncertain empirical determinations. We also compare the low energy phase sh ifts of the nn and the np system. We present a classification scheme for co rrections to the leading order results and show that power counting explain s previously made phenomenological observations. (C) 1999 Published by Else vier Science B.V. All rights reserved.