Subleading contributions to the three-nucleon contact interaction
  We obtain a minimal form of the two-derivative three-nucleon contact Lagrangian, by imposing all constraints deriving from discrete symmetries, Fierz identities and Poincare' covariance. The resulting interaction, depending on 13 unknown low-energy constants, leads to a three-nucleon potential which we give in a local form in configuration space. We also consider the leading (no-derivative) four-nucleon interaction and show that there exists only one independent operator. 
L. Girlanda (Salento U. and INFN, Lecce), A. Kievsky (INFN, Pisa) and   M. Viviani (INFN, Pisa)
nucl-th