Nuclear forces and their impact on neutron-rich nuclei and neutron-rich matter

Abstract: We review the impact of nuclear forces on matter at neutron-rich extremes. Recent results have shown that neutron-rich nuclei become increasingly sensitive to three-nucleon forces, which are at the forefront of theoretical developments based on effective field theories of quantum chromodynamics. This includes the formation of shell structure, the spectroscopy of exotic nuclei, and the location of the neutron dripline. Nuclear forces also constrain the properties of neutron-rich matter, including the neutron skin, the symmetry energy, and the structure of neutron stars. We first review our understanding of three-nucleon forces and show how chiral effective field theory makes unique predictions for many-body forces. Then, we survey results with three-nucleon forces in neutron-rich oxygen and calcium isotopes and neutron-rich matter, which have been explored with a range of many-body methods. Three-nucleon forces therefore provide an exciting link between theoretical, experimental and observational nuclear physics frontiers.

• The paper demonstrates that three-nucleon forces drive shell closures and set the neutron dripline in neutron-rich nuclei using chiral EFT techniques.
• The study employs ab initio methods like coupled-cluster theory and in-medium SRG to link microscopic nuclear interactions with macroscopic neutron star properties.
• The findings underscore that refining low-energy couplings in EFT enhances predictions of nuclear structure and neutron star equations of state.

Nuclear Forces and Their Impact on Neutron-Rich Nuclei and Neutron-Rich Matter

This paper explores the critical role of nuclear forces, especially three-nucleon (3N) forces, in understanding and predicting the behavior of neutron-rich nuclei and neutron-rich matter. The authors review recent advancements in effective field theories of quantum chromodynamics and their application to theoretical nuclear physics. The discussion spans topics from shell structure formation in neutron-rich nuclei to the characteristics of neutron stars, illustrating the extensive implications of 3N forces in both experimental and observational research domains.

The paper highlights how neutron-rich nuclei, such as those found in the oxygen and calcium isotopic chains, are increasingly sensitive to 3N forces. These forces are pivotal for the emergence of shell closures, the determination of the neutron dripline, and the spectroscopy of exotic nuclei. Furthermore, through the use of chiral effective field theory (EFT), the authors present unique predictions regarding many-body forces up to next-to-next-to-next-to-leading order (N$^3$LO) with a minimal number of new low-energy couplings.

Neutron-rich matter's properties, especially at nuclear densities, are influenced significantly by 3N forces. The neutron skin thickness, symmetry energy, and neutron star structure are all sensitive to the interactions within these dense nuclear systems. The authors utilize various ab initio methods, such as coupled-cluster theory, in-medium similarity renormalization group, and self-consistent Green’s functions, to study the evolving properties of neutron-rich isotopes.

Among the significant numerical results, the paper underscores the repulsive nature of 3N forces in neutron matter, which leads to increased pressure and consequently influences large-scale astrophysical phenomena. This aligns with findings on neutron star structure and supports robust predictions concerning neutron star radii and equation of state constraints. Furthermore, comparisons between theoretical calculations and experimental neutron-rich isotope data reveal that 3N forces are instrumental in overcoming deficiencies observed when solely NN interactions are considered.

The implications of this research are broad, suggesting that a deeper understanding of these nuclear forces could lead to advancements in nuclear theory and experimental techniques. The connections drawn between microscopic nuclear interactions and macroscopic astrophysical observations could foster enhanced models for predicting nuclear behavior under extreme conditions, such as those found in the cores of neutron stars.

Future developments in this field could involve more systematic studies of chiral EFT convergence, improving the accuracy of theoretical predictions by refining low-energy coupling estimates, and exploring the boundaries of current nuclear force models. In addition, continued progress in experimental techniques at rare isotope facilities may offer further insights into the nuanced interplay between nuclear forces, shedding light on both terrestrial and cosmic phenomena. These efforts collectively hold promise for advancing both theoretical and practical aspects of nuclear physics.