With the goal of developing predictive ab-initio capability for light and medium-mass nuclei, twonucleon and three-nucleon forces from chiral effective field theory are optimized simultaneously to low-energy nucleon-nucleon scattering data, as well as binding energies and radii of few-nucleon systems and selected isotopes of carbon and oxygen. Coupled-cluster calculations based on this interaction, named NNLOsat, yield accurate binding energies and radii of nuclei up to 40 Ca, and are consistent with the empirical saturation point of symmetric nuclear matter. In addition, the low-lying collective J π = 3 − states in 16 O and 40 Ca are described accurately, while spectra for selected p-and sd-shell nuclei are in reasonable agreement with experiment. Introduction -Interactions from chiral effective field theory (EFT) [1][2][3][4] and modern applications of renormalization group techniques [5][6][7][8] have opened the door for a description of atomic nuclei consistent with the underlying symmetries of quantum chromodynamics, the theory of the strong interaction. Chiral nuclear forces can be constructed systematically from long-range pion physics augmented by contact interactions. Over the past decade, the renaissance of nuclear theory based on realistic nuclear forces and powerful computational methods has pushed the frontier of ab initio calculations from fewbody systems and light nuclei [6, 9, 10] to medium-mass nuclei [11][12][13][14][15][16][17][18][19].

SummaryWhat is the size of the atomic nucleus? This deceivably simple question is difficult to answer. While the electric charge distributions in atomic nuclei were measured accurately already half a century ago, our knowledge of the distribution of neutrons is still deficient. In addition to constraining the size of atomic nuclei, the neutron distribution also impacts the number of nuclei that can exist and the size of neutron stars. We present an ab initio calculation of the neutron distribution of the neutron-rich nucleus 48 Ca. We show that the neutron skin (difference between radii of neutron and proton distributions) is significantly smaller than previously thought. We also make predictions for the electric dipole polarizability and the weak form factor; both quantities are currently targeted by precision measurements. Based on ab initio results for 48 Ca, we provide a constraint on the size of a neutron star.

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Despite being a complex many-body system, the atomic nucleus exhibits simple structures for certain ‘magic’ numbers of protons and neutrons. The calcium chain in particular is both unique and puzzling: evidence of doubly magic features are known in ^40,48Ca, and recently suggested in two radioactive isotopes, ^52,54Ca. Although many properties of experimentally known calcium isotopes have been successfully described by nuclear theory, it is still a challenge to predict the evolution of their charge radii. Here we present the first measurements of the charge radii of ^49,51,52Ca, obtained from laser spectroscopy experiments at ISOLDE, CERN. The experimental results are complemented by state-of-the-art theoretical calculations. The large and unexpected increase of the size of the neutron-rich calcium isotopes beyond N = 28 challenges the doubly magic nature of 52Ca and opens new intriguing questions on the evolution of nuclear sizes away from stability, which are of importance for our understanding of neutron-rich atomic nuclei