NN scattering S-3(1)-D-3(1) mixing angle at next-to-next-to-leading order - art. no. 044005

The S-3(1)-D-3(1) mixing angle for nucleon-nucleon scattering epsilon(1) is calculated to next-to-next-to-leading order in an effective field theory w ith perturbative pions. Without pions, the low energy theory fits the obser ved epsilon(1) well for momenta less than similar to 50 MeV. Including pion s perturbatively significantly improves the agreement with data for momenta up to similar to 150 MeV with one less parameter. Furthermore, for these m omenta the accuracy of our calculation is similar to an effective field the ory calculation in which the pion is treated nonperturbatively. This gives phenomenological support for a perturbative treatment of pions in low energ y two-nucleon processes. We explain why it is necessary to perform spin and isospin traces in d dimensions when regulating divergences with dimensiona l regularization in higher partial wave amplitudes.