Emergence of Simple Patterns in Complex Atomic Nuclei from First Principles

Abstract

Abstract. We study the structure of low-lying states in 6 Li, 6 He, 8 Be, 8 B, 12 C, and 16 O, using ab initio symmetry-adapted no-core shell model. The results of our study demonstrate that collective modes in light nuclei emerge from first principles. We investigate the impact of the symmetry-adapted model space on spectroscopic properties and, in the case of the ground state of 6 Li, on elastic electron scattering charge form factor. The results confirm that only a small symmetry-adapted subspace of the complete model space is needed to accurately reproduce complete-space observables and the form factor momentum dependence. IntroductionAb initio approaches to nuclear structure and reactions have advanced our understanding and capability of achieving first-principle descriptions of light nuclei [1,2,3]. These advances are driven by the major progress in the development of realistic nuclear potential models, such as J-matrix inverse scattering potentials [4] and two-and three-nucleon potentials derived from meson exchange theory [5] or by using chiral effective field theory [6], and, at the same time, by the utilization of massively parallel computing resources [7,8,9]. The ab initio applications to heavier systems has been hindered by computational challenges. While the Coupled Cluster [10] and selfconsistent Greens function methods [11] can be applied to probe medium-mass nuclei in the vicinity of shell closures, for nuclei far from closures, innovative approaches has just started to emerge [12]. These new developments place serious demands on available computational resources. This points to the need of further major advances in many-body methods to access a wider range of nuclei and experimental observables, while retaining the predictive power of ab initio methods, which makes them suitable for e.g. targeting short-lived nuclei that are inaccessible by experiment but essential to further modeling, for example, of the dynamics of X-ray bursts and the path of nucleosynthesis (see, e.g., [13,14]).The main challenge of ab initio configuration-interaction approaches is inherently coupled