How many-body correlations and $\alpha$-clustering shape $^6$He

TL;DR

This paper demonstrates that including alpha-cluster degrees of freedom and many-body correlations in ab initio calculations effectively reproduces the properties of the Borromean nucleus $^6$He, highlighting the importance of clustering and correlations.

Contribution

It introduces a method that incorporates $^4$He+$n$+$n$ cluster degrees of freedom into ab initio calculations, improving the description of $^6$He.

Findings

Supplementing the model space with cluster degrees of freedom improves binding energy predictions.

Alpha-clustering and many-body correlations are crucial for accurate $^6$He modeling.

The energy spectrum depends on the interaction's resolution scale.

Abstract

The Borromean $^6$He nucleus is an exotic system characterized by two `halo' neutrons orbiting around a compact $^4$He (or $\alpha$) core, in which the binary subsystems are unbound. The simultaneous reproduction of its small binding energy and extended matter and point-proton radii has been a challenge for {\em ab initio} theoretical calculations based on traditional bound-state methods. Using soft nucleon-nucleon interactions based on chiral effective field theory potentials, we show that supplementing the model space with $^4$He+$n$+$n$ cluster degrees of freedom largely solves this issue. We analyze the role played by the $\alpha$-clustering and many-body correlations, and study the dependence of the energy spectrum on the resolution scale of the interaction.