2-PION EXCHANGE AND CHIRAL-SYMMETRY RESTORATION

The scalar, isoscalar piece of the two-pion exchange force between two nucleons is calculated in the linear sigma model. A large contributio n to this force is found to come from terms involving direct coupling of the sigma field to the nucleons. This part of the interaction can b e related to the partial restoration of chiral symmetry experienced by a nucleon in nuclear matter, and it has a strength determined by the sigma commutator. Even if the ''elementary'' sigma is taken to be heav y (m(sigma) > 1 GeV), the effect has a longer range, determined by the mass of the pair of pions. Although the sigma fields used in relativi stic models of nuclei have a similar strength and range, no simple rel ationship is found between such fields and partial restoration of chir al symmetry.