Advances in the Ab Initio Description of Neutron-Rich Nuclei

Today, computationally efficient many-body methods can be used to perform first-principles calculations for nuclei as heavy as the tin isotopes. This progress has made it possible to confront modern two- and three-nucleon interactions from Chiral Effective Field Theory (EFT) with a wealth of experimental data, in particular for neutron-rich nuclei, and provide important guidance in their ongoing refinement. Significant challenges remain when it comes to the treatment of collective correlations in doubly open-shell nuclei (e.g., due to intrinsic deformation) or the coupling to the continuum\footnote{S. R. Stroberg, H. Hergert, S. K. Bogner and J. D. Holt, Ann. Rev. Nucl. Part. Sci. 69, 307 (2019)}. These issues have sparked new lines of research about combining complementary techniques, e.g., particle-hole expansions with symmetry breaking and restoration. The In-Medium Similarity Renormalization Group (IMSRG) offers a particular useful framework for such efforts$^{2,}$\footnote{H. Hergert, S. K. Bogner, T. D. Morris, A. Schwenk and K. Tsukiyama, Phys. Rept. 621, 165 (2016)}$^{,}$\footnote{H. Hergert, Phys. Scripta 92, 023002 (2017)}. I will give a brief overview of the state of the art of \emph{Ab initio} nuclear many-body theory, and discuss applications of “hybrid” IMSRG approaches$^{2,}$\footnote{E. Gebrerufael, K. Vobig, H. Hergert and R. Roth, Phys. Rev. Lett. 118, 152503 (2017) }$^{,}$\footnote{J. M. Yao, B. Bally, J. Engel, T. R. Rodriguez and H. Hergert, Phys. Rev. Lett. 124, 232501 (2020)} to the first-principles description of selected medium-mass open-shell nuclei, including candidates for fundamental symmetry tests$^{6}$.