Unitary ambiguity of NN contact interactions and the 3N force

Understand

We identify a redundancy between two- and three-nucleon contact interactions at the fourth and fifth order of the chiral expansion respectively.

• In particular we show that tensor-type and spin-orbit three-nucleon contact interactions effectively account for that part of the two-nucleon interaction which depends on the total center-of-mass momentum and is unconstrained by relativity.
• This might give the chiral effective field theory enough flexibility to successfully address $A=3$ scattering observables already at N3LO.