Nuclear Potential with Two Pion Exchange
  We carefully calculate the nucleon-nucleon interaction due to two pion exchange processes by properly evaluating the corresponding Feynman diagrams. In the estimation, we have made no approximation, and instead, we carry out the numerical integrations of three Feynman parameters. It is found that the two pion exchange potential gives rise to the attractive force which corresponds to the effective scalar meson with its mass of $m_s\simeq 4.7 m_\pi$ and its strength of ${g_s^2\over 4\pi}\simeq 1.45 $. There is a strong isospin dependence of $(\bm{\tau}_1\cdot \bm{\tau}_2)^2 $ which cannot be simulated by the one boson exchange model calculations. 
Takehisa Fujita, Naohiro Kanda and Sachiko Oshima
nucl-th