$\sigma$ Exchange in the NN Interaction within the Chiral Unitary   Approach
  We study the nucleon-nucleon interaction in the isoscalar-scalar channel using t he chiral unitary approach. The $t$-matrix of the pion-pion scattering in this c hannel is summed up to all orders using the B-S equation. We find that the calcu lated results at long distances are close to those of the $\sigma$-exchange inte raction. In addition, there appears a shorter range repulsion in this channel. 
E. Oset, H. Toki, M. Mizobe and T. T. Takahashi