The Nuclear Sigma Term in the Skyrme Model: Pion-Nucleus Interaction
  The nuclear sigma term is calculated including the nuclear matrix element of the derivative of the NN interaction with respect to the quark mass, $m_q\frac{\partial V_{NN}}{\partial m_q}$. The NN potential is evaluated in the skyrmion-skyrmion picture within the quantized product ansatz. The contribution of the NN potential to the nuclear sigma term provides repulsion to the pion-nucleus interaction. The strength of the s-wave pion-nucleus optical potential is estimated including such contribution. The results are consistent with the analysis of the experimental data. 
A.Gammal (Instituto de Fisica da Universidade de Sao Paulo) and T.   Frederico (Departamento de Fisica,ITA, Centro Tecnico A...