How chiral forces shape neutron-rich Ne and Mg nuclei

We compute the structure of the exotic even nuclei ${}^{20-34}$Ne and ${}^{34-40}$Mg using interactions from chiral effective field theory (EFT). Our results for the ground-state rotational bands in ${}^{20-32}$Ne and ${}^{36-40}$Mg agree with data. We predict a well-deformed ${}^{34}$Ne and find that ${}^{40}$Mg exhibits an oblate deformed band close to the prolate ground-state, indicating the emergence of shape co-existence at the neutron dripline. A global sensitivity analysis shows that the subleading singlet $S$-wave contact and a pion-nucleon coupling strongly impact deformation in chiral EFT.