one scalar meson associated with the diagrams of fig. 1a. In principle the scalar coupling constants predicted by these Lagrangians could be different. However, we are interested only in dynamical distinctions between the sigma and the chiral scalar and, from now on, we set $g_s=g$ in order to force both models to simulate exactly the same two-body potential.

On the other hand, these models produce different predictions for the effective $\pi NN$ vertex and in this section we consider the form of this interaction. The basic ingredients are the amplitudes $T_\sigma $ and $T_s$, that describe the processes $\pi N\rightarrow \sigma N$ and $\pi
N\rightarrow SN$ respectively. The amplitude $T_\sigma $ is determined by just the first two diagrams of fig. 4a whereas $T_s$ also includes the seagull term. As the calculations of $T_\sigma $ and $T_s$ are quite similar, we denote both amplitudes by $T$ and identify the seagull contribution by a parameter $\lambda $, such that $T_\sigma =T\left( \lambda
=0\right) $ and $T_s=T\left( \lambda =1\right) $. At tree level, $T$ is given by the diagrams depicted in fig 4a, and we have

$$T\left( \lambda \right) =-ig^2\tau _c\bar u\left( {\mbox{\boldmath $p'$}}\right)
\left[ \frac{\not{p}_d+m}{p_d^2-m^2}\gamma _5+\gamma _5\frac{\not{p}_x+m}{p_x^2-m^2}
+\frac \lambda {gf_\pi }\gamma 