Δ isobars and nuclear saturation

We construct a nuclear interaction in chiral effective field theory with explicit inclusion of the Delta-isobar Delta(1232) degree of freedom at all orders up to next-to-next-to-leading order (NNLO). We use pion-nucleon (pi N) low-energy constants (LECs) from a Roy-Steiner analysis of pi N scattering data, optimize the LECs in the contact potentials up to NNLO to reproduce low-energy nucleon-nucleon scattering phase shifts, and constrain the three-nucleon interaction at NNLO to reproduce the binding energy and point-proton radius of He-4. For heavier nuclei we use the coupled-cluster method to compute binding energies, radii, and neutron skins. We find that radii and binding energies are much improved for interactions with explicit inclusion of Delta(1232), while Delta-less interactions produce nuclei that are not bound with respect to breakup into alpha particles. The saturation of nuclear matter is significantly improved, and its symmetry energy is consistent with empirical estimates.