Scalar form factors and nuclear interactions
  The scalar-isoscalar term in the two-pion exchange $NN$ potential is abnormally large and does not respect the hierarchy of effects predicted by chiral perturbation theory. We argue that this anomaly is associated with non-perturbative effects, which are also present in the $\pi N$ scalar form factor. 
M. R. Robilotta and G. R. S. Zarnauskas