Three- and Four-Nucleon Systems from Chiral Effective Field Theory

Recently developed chiral nucleon-nucleon $\left(\mathrm{NN}\right)$ forces at next-to-leading order (NLO), that describe $\mathrm{NN}$ phase shifts up to about 100 MeV fairly well, have been applied to $3N$ and $4N$ systems. Faddeev-Yakubovsky equations have been solved rigorously. The resulting $3N$ and $4N$ binding energies are in the same range as found using standard $\mathrm{NN}$ potentials. In addition, low-energy $3N$ scattering observables are very well reproduced as for standard $\mathrm{NN}$ forces. The long-standing $A_y$ puzzle is absent at NLO. The cutoff dependence of the scattering observables is rather weak.