Optimized Chiral Nucleon-Nucleon Interaction at Next-to-Next-to-Leading Order

We optimize the nucleon-nucleon interaction from chiral effective field theory at next-to-next-to-leading order (NNLO). The resulting new chiral force ${\mathrm{NNLO}}_{\mathrm{opt}}$ yields ${\chi }^2\approx 1$ per degree of freedom for laboratory energies below approximately 125 MeV. In the $A=3$, 4 nucleon systems, the contributions of three-nucleon forces are smaller than for previous parametrizations of chiral interactions. We use ${\mathrm{NNLO}}_{\mathrm{opt}}$ to study properties of key nuclei and neutron matter, and we demonstrate that many aspects of nuclear structure can be understood in terms of this nucleon-nucleon interaction, without explicitly invoking three-nucleon forces.