More Effective Field Theory for Nonrelativistic Scattering

An effective field theory treatment of nucleon-nucleon scattering at low energy shows much promise and could prove a useful tool in the study of nuclear matter at both ordinary and extreme densities. The analysis is complicated by the existence a large length scale --- the scattering length --- which arises due to couplings in the short distance theory being near critical values. I show how this can be dealt with by introducing an explicit s-channel state in the effective field theory. The procedure is worked out analytically in a toy example. I then demonstrate that a simple effective field theory excellently reproduces the 1S_0 np phase shift up to the pion production threshold.