Ab initio theory and limits of existence*

Ab initio methods have made significant strides in extending regions of applicability into the medium and heavy mass regions of the nuclear chart.  At the same time, there has been considerable work on providing rigorous uncertainty quantifications on theoretical calculations to enable more meaningful comparison and integration with experiment.  Such advances are key for understanding nuclei at the extremes of existence where experimental data is limited.  However, near the limits of existence, accurate descriptions of nuclei remain a significant challenge, even in light nuclei.  In nuclei far from stability, structure is complicated by the competition between single particle structure and collectivity, which gives rise to e.g., shape coexistence, parity inversion, and intruder states.  The emergence of these phenomena impacts transition probabilities, lifetimes, radii, cross sections etc.  In this talk I will highlight advances in ab initio nuclear theory in understanding nuclei far from stability and discuss ongoing challenges in providing accurate descriptions of nuclei at the limits of existence.