Spin observables in nucleon-deuteron scattering and three-nucleon forces

Three-nucleon forces, which compose an up-to-date subject in few-nucleon systems, provide a good account of the triton binding energy and the cross section minimum in proton-deuteron elastic scattering. However, three-nucleon forces do not explain spin observables such as the nucleon and deuteron analyzing powers, suggesting serious defects in their spin dependence. We study the spin structure of nucleon-deuteron elastic amplitudes by decomposing them into spin-space tensors and examine effects of three-nucleon forces to each component of the amplitudes obtained by solving the Faddeev equation. Assuming that the spin-scalar amplitudes dominate the others, we derive simple expressions for spin observables in the nucleon-deuteron elastic scattering. The expressions suggest that a particular combination of spin observables in the scattering provides direct information on scalar, vector, or tensor component of the three-nucleon forces. These effects are numerically investigated by the Faddeev calculation.