Physicists crack the code of unstable nuclear resonances with groundbreaking method

A team of nuclear physicists has made a significant breakthrough in predicting broad resonances—complex energy states that have long posed computational challenges. By extending the eigenvector continuation method into complex-energy space, researchers can now model unstable nuclei more efficiently and with greater accuracy. The findings promise to deepen understanding of exotic nuclear systems and their roles in astrophysical processes.

The study, led by Rongzhe Hu, Nicolas Michel, Zhicheng Xu, Jianguo Li, and Furong Xu, tackles a persistent problem in nuclear theory: the instability of calculations involving broad resonances. These resonances, found in nuclei like hydrogen, helium-6, helium-8, and four-neutron systems, often disrupt traditional computational methods. The team's solution builds on the eigenvector continuation approach, which predicts solutions for large-scale many-body problems using only a few known bound and narrow resonance states.

Applying this method in complex-energy space allows researchers to bypass previous limitations. They successfully analysed 12 different exotic nuclear systems, including halo nuclei—unusual structures where protons or neutrons orbit far from the core. These nuclei, such as helium-6, exhibit rare decay modes and play key roles in stellar processes where heavy elements form.

The work also bridges two major theoretical frameworks: the Gamow Shell Model and ab initio methods. The Gamow Shell Model specialises in describing unstable nuclei by solving the Schrödinger equation for all proton-neutron interactions. By combining it with ab initio techniques, which derive properties from fundamental nuclear forces, the team achieves a more complete picture of nuclear behaviour. This convergence helps refine models of the strong nuclear force that binds protons and neutrons together.

The extended eigenvector continuation method now enables stable calculations of broad resonances, opening new avenues for studying exotic nuclei. These advancements will improve the accuracy of nuclear reaction models, particularly for light and unstable isotopes. The findings also support ongoing research into astrophysical environments where such nuclei are produced.