Two-pion exchange and chiral symmetry restoration

The scalar, isoscalar piece of the two-pion exchange force between two nucleons is calculated in the linear {σ} model. A large contribution to this force is found to come from terms involving direct coupling of the {σ} field to the nucleons. This part of the interaction can be related to the partial restoration of chiral symmetry experienced by a nucleon in nuclear matter, and it has a strength determined by the {σ} commutator. Even if the ``elementary'' {σ} is taken to be heavy (m_σ>1GeV), the effect has a longer range, determined by the mass of the pair of pions. Although the {σ} fields used in relativistic models of nuclei have a similar strength and range, no simple relationship is found between such fields and partial restoration of chiral symmetry.