Ab initio lattice study of neutron–alpha scattering with chiral forces at N3LO

We present the first ab initio lattice calculation of neutron–alpha (n–α) scattering using nuclear lattice effective field theory with chiral interactions at next-to-next-to-next-to-leading order (N3LO). Building on the high-fidelity chiral Hamiltonian introduced in Elhatisari et al (2024 Nature 630 59), we compute scattering phase shifts in the S- and P-wave channels using the Lüscher finite-volume method. Our results demonstrate excellent agreement with empirical R-matrix phase shifts in the ²S_1/2 and ²P_3/2 channels, while revealing persistent discrepancies in the ²P_1/2 channel for neutron energies above 5 MeV. To systematically investigate these discrepancies, we construct and analyze a simplified neutron–alpha toy model, demonstrating that these discrepancies are not due to the use of the Lüscher finite-volume method. Additionally, we revisit our three-nucleon (3N) force fitting procedure, explicitly incorporating neutron–alpha scattering data through comprehensive Markov Chain Monte Carlo sampling. This analysis confirms the stability of nuclear binding-energy predictions and highlights the need for further refinements in the lattice N3LO three-nucleon forces to fully describe neutron–alpha scattering in the challenging ²P_1/2 channel.