Meson production in proton-proton scattering within an extended linear   sigma model
  We study the production of non-strange mesons in proton-proton scattering reactions within an effective model of mesons and baryons with global chiral symmetry. The model includes the nucleon ($N$) and its chiral partner ($N^{\ast}$) and their couplings to the $N_{f}=2$ multiplets of (pseudo-)scalar and (axial-)vector mesons. Results for the production of $\omega$ and $\eta$ mesons are presented. 
Khaled Teilab, Francesco Giacosa and Dirk H. Rischke
nucl-th hep-ph