A unitary transformation allows to remove redundant terms in the two-nucleon ($2N$) contact interaction at the fourth order (N3LO) in the low-energy expansion of chiral effective field theory. In so doing a three-nucleon ($3N$) interaction is generated. We express its short-range component in terms of five combinations of low-energy constants (LECs) parametrizing the N3LO $2N$ contact Lagrangian. Within a hybrid approach, in which this interaction is considered in conjunction with the phenomenological AV18 $2N$ potential, we show that the involved LECs can be used to fit very accurate data on polarization observables of low-energy $p\text{−}d$ scattering, in particular the $A_y$ asymmetry. The resulting interaction is of the right order of magnitude for a N3LO contribution.

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• Elastic scattering reactions
• Few-body systems
• Models based on symmetries
• Nuclear forces
• Nuclear reactions
• Nucleon-nucleon interactions