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 ${}^{28}\mathrm{O}$ is stable with respect to ${}^{24}\mathrm{O}$, while calculations with a momentum cutoff of 600 MeV result in a slightly unbound ${}^{28}\mathrm{O}$. 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 ${}^{28}\mathrm{O}$ cannot be ruled out from ab initio calculations, and that three-nucleon forces and continuum effects play the dominant role in deciding this question.

Figure 1

Binding energy [within ΛCCSD(T)] for ${}^{24}\mathrm{O}$ from a chiral $\mathit{NN}$ potential at order N${}^3\mathrm{LO}$ with high-momentum cutoffs ${\Lambda }_{\chi }=500$ MeV as a function of the oscillator spacing $\hslash \omega$ and the size of the model space.

Figure 2

Same as Fig. 1, except for ${}^{28}\mathrm{O}$ and a chiral cutoff ${\Lambda }_{\chi }=600$ MeV.

Figure 3

Ground-state energies of neutron-rich oxygen isotopes ${}^A$O relative to ${}^{22}\mathrm{O}$ for chiral interactions with two different cutoffs ${\Lambda }_{\chi }$.