Rigorous constraints on three-nucleon forces in chiral effective field theory from fast and accurate calculations of few-body observables

We explore the constraints on the three-nucleon force (3NF) of chiral effective field theory (xEFT) that are provided by bound-state observables in the A = 3 and A = 4 sectors. Our statistically rigorous analysis incorporates experimental error, computational method uncertainty, and the uncertainty due to truncation of the xEFT expansion at next-to-next-to-leading order. A consistent solution for the 3H binding energy, the 4He binding energy and radius, and the 3H I3-decay rate can only be obtained if xEFT truncation errors are included in the analysis. The I3-decay rate is the only one of these that yields a nondegenerate constraint on the 3NF low-energy constants, which makes it crucial for the parameter estimation. We use eigenvector continuation for fast and accurate emulation of no-core shell model calculations of the few-nucleon observables. This facilitates sampling of the posterior probability distribution, allowing us to also determine the distributions of the parameters that quantify the truncation error. We find a xEFT expansion parameter of Q = 0.33 +/- 0.06 for these observables.

Automated summary

This study explores the constraints on the three-nucleon force (3NF) of chiral effective field theory (xEFT) by incorporating experimental error, computational method uncertainty, and the uncertainty due to truncation of the xEFT expansion at next-to-next-to-leading order. Including xEFT truncation errors in the analysis is crucial for obtaining a consistent solution for the binding energy and decay rate of certain nuclear states. The findings suggest an xEFT expansion parameter of Q = 0.33 +/- 0.06 for the observed nuclear properties.