Phenomenological spin-orbit three-body force

In order to improve the description of the N-d vector analyzing powers $A_y$ and ${\mathrm{iT}}_{11}$ (the so-called $A_y$ puzzle) a spin-orbit three-body force has been introduced. The $\mathbf{L}\cdot \mathbf{S}$ term in the $\mathrm{NN}$ potential has been modified including a two-parameter three-body function depending on the hyperradius $\rho$. The modification has been performed in channels where the pair of nucleons $\mathrm{}(i,j)\mathrm{}$ are coupled to spin $S_{\mathrm{ij}}=1\mathrm{}$ and isospin $T_{\mathrm{ij}}=1\mathrm{}$. Calculations have been done in the energy region from $E_{\mathrm{lab}}=648\mathrm{}$ keV up to $E_{\mathrm{lab}}=10\mathrm{}$ MeV. A noticeable improvement in the description of the polarization observables has been obtained.