Nd scattering and the Ay puzzle to next-to-next-to-next-to-leading order
Polarization observables in neutron-deuteron scattering are calculated to next-to-next-to-next-to-leading order (N3LO) in pionless effective field theory (EFT¬π). At N3LO the two-body P-wave contact interactions are found to be important contributions to the neutron vector analyzing power, Ay(θ), and the deuteron vector analyzing power, iT11(θ). Extracting the two-body P-wave EFT¬π coefficients from two-body scattering data and varying them within the expected EFT¬π theoretical errors provides results that are consistent (at the N3LO level) with Ay experimental data at low energies. Cutoff dependence of the N3LO correction of the doublet S-wave nd scattering amplitude suggests the need for a new three-body force at N3LO, which is likely one that mixes Wigner-symmetric and Wigner-antisymmetric three-body channels.