Abstract:
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.