Fleming, S; Mehen, T; Stewart, IW, *The NN Scattering $^3S_1-{}^3D_1$ Mixing Angle at NNLO*,
Phys. Rev. C, vol. 61 no. 4
(2000),
pp. 044005 .
**Abstract:**

*The 3S1-3D1 mixing angle for nucleon-nucleon scattering,
epsilon_1, is calculated to next-to-next-to-leading order in
an effective field theory with perturbative pions. Without
pions, the low energy theory fits the observed epsilon_1
well for momenta less than $\sim 50$ MeV. Including pions
perturbatively significantly improves the agreement with
data for momenta up to $\sim 150$ MeV with one less
parameter. Furthermore, for these momenta the accuracy of
our calculation is similar to an effective field theory
calculation in which the pion is treated non-perturbatively.
This gives phenomenological support for a perturbative
treatment of pions in low energy two-nucleon processes. We
explain why it is necessary to perform spin and isospin
traces in d dimensions when regulating divergences with
dimensional regularization in higher partial wave amplitudes.*