Wigner symmetry in the limit of large scattering lengths

We note that in the limit where the NN 1S0 and 3S1 scattering lengths, a^(1S0) and a^(3S1), go to infinity, the leading terms in the effective field theory for strong NN interactions are invariant under Wigner's SU(4) spin-isospin symmetry. This explains why the leading effects of radiation pions on the S-wave NN scattering amplitudes vanish as a^(1S0) and a^(3S1) go to infinity. The implications of Wigner symmetry for NN to NN axion and gamma d to n p are also considered.