THE REACTIONS PP-]PP-PI(0) AND PP-]D-PI(- THE ROLE OF THE ISOSCALAR PI-N SCATTERING-AMPLITUDE() AT THRESHOLD )

We examine the role of the elementary isoscalar pion-nucleon scatterin g amplitude in the description of the processes pp-->pp pi(o) and pp-- >d pi(+) at threshold. We argue that the presently used tree level dim ension two approximation used in chiral perturbation theory is insuffi cient as input by direct comparison with the pi N scattering data. We also show that a successful semi-phenomenological boson-exchange model does better in the description of these data. The influence of the vi olation of crossing symmetry in the meson-exchange model has to be stu died in more detail. We stress that further investigations of the proc ess pp --> d pi(+) can pave the way to a deeper understanding of the p ion dominated part of the transition operator. (C) 1998 Elsevier Scien ce B.V.