Scalar meson production in nucleon-nucleon collisions near threshold

We establish the model-independent spin structure of the matrix elements for the near-threshold scalar meson production in $pp-$ and $np$-collisions, when the final particles are emitted in S-state. Polarization phenomena are derived in a general form. The properties of the $t-$channel dynamics, which is based on different meson exchanges, are studied in terms of the $s-$channel parametrization of the matrix element. The prediction of a 'realistic' model, based on $\pi+\sigma$-exchanges are also presented.