Relativity and the low energy nd Ay puzzle

TL;DR

This paper solves the relativistic three-nucleon problem exactly, revealing that relativistic effects are minimal above 20 MeV but influence analyzing power at lower energies, suggesting the need for stronger three-nucleon forces.

Contribution

It provides an exact Poincare invariant solution to the three-nucleon problem with a relativistic interaction equivalent to high-precision models, highlighting the impact on analyzing power.

Findings

Relativistic effects are negligible above 20 MeV.

Below 20 MeV, dynamical effects reduce the analyzing power maximum by up to 10%.

Three-nucleon forces likely need to be stronger to match experimental data.

Abstract

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