Quantifying uncertainties due to irreducible three-body forces in deuteron-nucleus reactions

Deuteron-induced nuclear reactions can be described within a three-body model consisting of a neutron, proton, and the nucleus interacting through pairwise forces. While Faddeev techniques enable the exact description of the three-body dynamics, their predictive power is limited in part by irreducibe three-body nucleon-nucleon-nucleus forces. Our goal is to use ab initio reaction theory to quantify the impact of the irreducible three-body force on bound state properties and scattering observables for light deuteron-nucleus systems. We adopt the no-core shell model (NCSM) coupled with the resonating group method (RGM) to compute effective nucleon-nucleus interactions and construct a three-body Hamiltonian from the pairwise interactions. We present momentum space Faddeev for deuteron-nucleus systems starting with ²H+⁴He. The bound state energies and cross sections obtained directly from the NCSM/RGM significantly differ from the Faddeev calculations, owing to the irreducible three-body force. We deduce that the latter arises from two-nucleon nucleons exchange terms in the deuteron-nucleus interaction.