The Ay puzzle and the nuclear force

The nucleon-deuteron analyzing power A, in elastic nucleon-deuteron scattering poses a longstanding puzzle. At energies E-lab below approximately 30 MeV A, cannot be described by any realistic nucleon-nucleon (NN) force. The inclusion of existing three-nucleon forces does not improve the situation. Because of recent questions about the P-3(J) NN phases, we examine whether reasonable changes in the NN force can resolve the puzzle. In order to do this we investigate the effect on the P-3(J) waves produced by changes in different parts of the potential (viz., the central force, tenser force, etc.), as well as on the two-body observables and on A(gamma). We find that it is not possible with reasonable changes in the NN potential to increase the three-body A(gamma) and at the same time to keep the two-body observables unchanged. We therefore conclude that the A(gamma) puzzle is likely to be solved by new three-nucleon forces, such as those of the spin-orbit type, which have not yet been taken into account.