Phenomenological theory of clustering at the nuclear surface and symmetry energy

TL;DR

This paper develops a phenomenological model of nuclei that includes surface clustering and explains the large symmetry energy at low densities, linking clustering, three-nucleon interactions, and neutron skin thickness.

Contribution

It introduces a general phenomenological framework incorporating clustering at the nuclear surface, explaining symmetry energy behavior and neutron skin reduction.

Findings

Large symmetry energy at low densities explained

Clustering reduces neutron skin thickness

Quartic term in symmetry energy is significant

Abstract

We present a phenomenological theory of nuclei which incorporates clustering at the nuclear surface in a general form. The theory explains the recently extracted large symmetry energy at low densities of nuclear matter and is consistent with the static properties of nuclei. In phenomenological way clusters of all sizes, shapes along with medium modifications are included. The importance of quartic term in symmetry energy is demonstrated at and below the equilibrium density in nuclear matter. It is shown that it is related both to clustering as well as to the contribution of three-nucleon interaction to the equation of state of neutron matter. Reasons for these are discussed. Due to clustering the neutron skin thickness in nuclei reduces significantly.