Three-nucleon contact interaction at the next-to-leading order

TL;DR

This paper develops a minimal three-nucleon contact interaction model within chiral effective theory, highlighting the need for subleading contact terms and examining the convergence of the pionful theory at higher orders.

Contribution

It constructs the minimal 3N contact Lagrangian with all symmetry constraints and derives pion-induced contributions to low-energy constants, revealing issues with convergence at higher orders.

Findings

Constructed 10 independent operators for the 3N contact Lagrangian.

Derived pion-induced contributions to low-energy constants.

Found no clear convergence signal between N2LO and N3LO.

Abstract

A satisfactory description of bound and scattering states of the three-nucleon (3N) system is still lacking, contrary to what happens in the two-nucleon case. In the framework of chiral effective theory, it is possible that a realistic 3N interaction will require the inclusion of subleading contact terms, which are unconstrained by chiral symmetry. We construct the minimal 3N contact Lagrangian imposing all constraints from the discrete symmetries, Fierz identities and Poincar\'e covariance, and show that it consists of 10 independent operators. By integrating out the pions from the effective theory we derive the pion-induced contributions to the corresponding low-energy constants (LECs), and find no clear signal of convergence of the pionful theory between N2LO and N3LO.