Chiral Symmetry and Peripheral Neutron- α Scattering

We propose and demonstrate that peripheral neutron-α scattering at low energies can serve as a sensitive and clean probe of the long-range three-nucleon forces. To this aim, we perform ab initio quantum Monte Carlo calculations using two- and three-nucleon interactions derived in chiral effective field theory up to third expansion order. We show that the longest-range three-nucleon force stemming from the two-pion exchange plays a crucial role in the proper description of the neutron-α D-wave phase shifts. Our Letter reveals the predictive power of chiral symmetry in the few-body sector and opens a new direction for probing and constraining three-nucleon forces.