Redundance of $\Delta$-isobar Parameters in Effective Field Theories
  It is shown that the off-shell parameters in the interaction Lagrangian of pions, nucleons, and $\Delta$-isobars are redundant in the framework of effective field theories. Our results also suggest the necessity of including the $\Delta$ as an explicit dynamical degree of freedom. 
Hua-Bin Tang and Paul J. Ellis