Relativity and the low-energy nd Ay puzzle

We solve the Faddeev equation in an exactly Poincare invariant formulation of the three-nucleon problem. The dynamical input is a relativistic nucleon-nucleon (NN) interaction that is exactly on-shell equivalent to the high-precision CD Bonn NN interaction. S-matrix cluster properties dictate how the two-body dynamics is embedded in the three-nucleon mass operator (rest Hamiltonian). We find that for neutron laboratory energies above approximate to 20 MeV relativistic effects on Ay are negligible. For energies below approximate to 20 MeV dynamical effects lower the nucleon analyzing power maximum slightly by approximate to 2% and Wigner rotations lower it further up to approximate to 10%, thereby increasing disagreement between data and theory. This indicates that three-nucleon forces (3NF) must provide an even larger increase of the Ay maximum than expected up to now.