Ab initio computation of neutron-rich oxygen isotopes

We compute the binding energy of neutron-rich oxygen isotopes and employ the coupled-cluster method and chiral nucleon-nucleon interactions at next-to-next-to-next-to-leading order with two different cutoffs. We obtain rather well-converged results in model spaces consisting of up to 21 oscillator shells. For interactions with a momentum cutoff of 500 MeV, we find that O28 is stable with respect to O24, while calculations with a momentum cutoff of 600 MeV result in a slightly unbound O28. The theoretical error estimates due to the omission of the three-nucleon forces and the truncation of excitations beyond three-particle-three-hole clusters indicate that the stability of O28 cannot be ruled out from ab initio calculations, and that three-nucleon forces and continuum effects play the dominant role in deciding this question.