Pion production in proton-proton collisions in a covariant one boson   exchange model
  Motivated by the renewed interest in studying the pion production on nuclei with protons at few GeV incident energies, we investigate the pion production in proton-proton collisions over an energy range of 300 $MeV$ to 2 $GeV$. Starting from a realistic one-boson exchange model with parameters fitted to the amplitudes of the elastic nucleon-nucleon scattering, we perform fully covariant calculations for the total, double and triple differential cross-sections of the $p(p,n\pi^+)p$ and $p(p,p\pi^0)p$ reactions. The calculations incorporate the exchange of $\pi, \rho,\omega$ and $\sigma$ mesons and treat nucleon and delta isobar as intermediate states. We obtain a reasonably good agreement with the experimental data in the entire range of beam energies. The form of the covariant delta propagator, the cut-off parameter for the $\pi NN$ and $\pi N\Delta$ vertex form factors and the energy dependence of the delta isobar decay width is investigated. 
A. Engel, A.K. Dutt-Mazumder, R. Shyam and U. Mosel