Universal geometry of two-neutron halos and Borromean Efimov states close to dissociation

TL;DR

This paper reveals universal geometric properties of two-neutron halo nuclei and Efimov states near dissociation, showing these properties apply broadly to excited states and regimes close to the three-body threshold.

Contribution

It analytically demonstrates the universal geometry of Borromean halos and Efimov states, extending previous effective-field theory results to excited states and non-resonant regimes.

Findings

Universal geometric properties apply to all Efimov states.

These properties persist away from resonance near the dissociation threshold.

Halo universality differs from Efimov universality, being more broadly applicable.

Abstract

The geometry of Borromean three-body halos, such as two-neutron halo nuclei or triatomic molecules close to dissociation, is investigated using a three-body model. This model enables to analytically derive the universal geometric properties found recently within an effective-field theory for halos made of a core and two resonantly-interacting particles [Phys. Rev. Lett., 128, 212501 (2022)]. It is shown that these properties not only apply to the ground three-body state, but also to all the excited (Efimov) states where the core-particle interaction is resonant. Furthermore, a universal geometry persists away from the resonant regime between the two particles, for any state close to the three-body threshold. This "halo universality" is different from the Efimov universality which is only approximate for the ground state. It is explained by the separability of the hyper-radius and hyper-angles close to the three-body dissociation threshold.