Delta Delta intermediate state in S-1(0) NN scattering from effective field theory

We examine the role of the Delta Delta intermediate state in NN scattering in the S-1(0) channel. The computation is performed at lowest order in an effective-field theory involving local four-fermion operators and one-pion exchange using dimensional regularization with minimal subtraction (<(MS)over bar>). As first discussed by Weinberg, in the theory with only nucleons, the large-scattering length in this channel requires a small scale for the local N-4 operators. When Delta's are included (but without pions) a large-scattering length can be obtained from operators with a scale root 2M(N)(M-Delta-M-N), but fine-tuning is required. The coefficients of the contact terms involving the Delta fields are not uniquely determined but for reasonable values one finds that, in general, NN scattering computed in the theory with Delta's looks like that computed in the theory without il's. The leading effect of the h's is to change the coefficients of the four-nucleon contact terms between the theories with and without Delta's. Further, the decoupling of the Delta's in the limit of large mass and strong coupling is clearly demonstrated. When pions are included, the typical scale for the contact terms is similar to 100 MeV, both with and root 2M(N)(M-Delta-M-N). For reasonable values of contact terms that reproduce the scattering length and effective range (at lowest order) the phase shift is not well reproduced over a larger momentum range as is found in the theory without h's at lowest order.