Incompressibility of neutron-rich matter

TL;DR

This paper investigates the saturation properties and incompressibility of neutron-rich matter using relativistic models, comparing numerical and analytic approaches, and proposing a hybrid model aligned with recent experimental data.

Contribution

It introduces a hybrid model for neutron-rich matter's incompressibility that aligns with experimental findings and highlights unresolved issues in the field.

Findings

Hybrid model better fits Sn-isotope data

Significant underestimation of strength in 208Pb by the hybrid model

Incompressibility of neutron-rich matter remains an open problem

Abstract

The saturation properties of neutron-rich matter are investigated in a relativistic mean-field formalism using two accurately calibrated models: NL3 and FSUGold. The saturation properties - density, binding energy per nucleon, and incompressibility coefficient - are calculated as a function of the neutron-proton asymmetry alpha=(N-Z)/A to all orders in alpha. Good agreement (at the 10% level or better) is found between these numerical calculations and analytic expansions that are given in terms of a handful of bulk parameters determined at saturation density. Using insights developed from the analytic approach and a general expression for the incompressibility coefficient of infinite neutron-rich matter, i.e., K0(alpha)=K0+Ktau*alpha^{2}+..., we construct a Hybrid model with values for K0 and Ktau as suggested by recent experimental findings. Whereas the Hybrid model provides a better description of the measured distribution of isoscalar monopole strength in the Sn-isotopes relative to both NL3 and FSUGold, it significantly underestimates the distribution of strength in 208Pb. Thus, we conclude that the incompressibility coefficient of neutron-rich matter remains an important open problem.