---
address:
- 'Instituto de Física Teórica, Univrsidade Estadual de São Paulo, Caixa Postal 875, 01405-900, São Paulo, SP, Brazil '
- 'FINPE,Instituto de Física, Universidade de São Paulo, Caixa Postal 66318, 05315-970, São Paulo, SP, Brazil'
author:
- 'C. M. Maekawa[^1]'
- 'M. R. Robilotta[^2]'
title: '$\sigma$-fields x Chiral Scalars in Nuclear Three Body Potentials'
---

epsf.sty

The scalar-isoscalar field of an effective chiral Lagrangian transforms differently in either linear or non-linear frameworks: in the former case it is the counterpart of the pion whereas in the latter it is chiral invariant on its own. We compare the predictions from these two models for nucleon interactions and find results which are identical for two-body and rather different for three-body potentials. Some qualitative features of three-body interactions are discussed.

Introduction
============

Since the fundamental work of Yukawa, the meson exchange theory has been successfully applied to the description of the nucleon-nucleon force. Nowadays it is well established that the one pion exchange potential (OPEP) is dominant at large distances, yielding a strong force with spin and isospin dependences.

The next layer of the interaction is associated with the exchange of two pions. This system has the lightest mass beyond the 