The reaction pi N -> pi pi N in chiral effective field theory with   explicit Delta(1232) degrees of freedom
  The reaction pi N -> pi pi N is studied at tree level up to next-to-leading order in the framework of manifestly covariant baryon chiral perturbation theory with explicit Delta(1232) degrees of freedom. Using total cross section data to determine the relevant low-energy constants, predictions are made for various differential as well as total cross sections at higher energies. A detailed comparison of results based on the heavy-baryon and relativistic formulations of chiral perturbation theory with and without explicit Delta degrees of freedom is given. 
D. Siemens, V. Bernard, E. Epelbaum, H. Krebs, Ulf-G. Mei{\ss}ner
nucl-th