High-order isospin-dependent surface tension contribution to the fourth-order symmetry energy of finite nuclei

TL;DR

This paper revisits the relationship between the fourth-order symmetry energy of nuclear matter and finite nuclei, emphasizing the importance of high-order isospin-dependent surface tension effects in accurate extraction and interpretation.

Contribution

It derives a comprehensive expression for the fourth-order symmetry energy of finite nuclei including high-order surface tension effects, clarifying previous misconceptions about its magnitude.

Findings

High-order surface tension significantly affects symmetry energy extraction.

Large measured $a_{sym,4}(A)$ values are compatible with small $E_{sym,4}( ho_0)$.

Derived expression for sixth-order symmetry energy involving higher-order parameters.

Abstract

The relation between the fourth-order symmetry energy $E_{\rm{sym,4}}(\rho_0)$ of nuclear matter at saturation density $\rho_0$ and its counterpart $a_{\rm{sym,4}}(A)$ of finite nuclei in a semiempirical nuclear mass formula is revisited by considering the high-order isospin-dependent surface tension contribution to the latter. We derive the full expression of $a_{\rm{sym,4}}(A)$, which includes explicitly the high-order isospin-dependent surface tension effects, and find that the value of $E_{\rm{sym,4}}(\rho_0)$ cannot be extracted from the measured $a_{\rm{sym,4}}(A)$ before the high-order surface tension is well constrained. Our results imply that a large $a_{\rm{sym,4}}(A)$ value of several MeVs obtained from analyzing nuclear masses can nicely agree with the empirical constraint of $E_{\rm{sym,4}}(\rho_0)\lesssim 2$ MeV from mean-field models and does not necessarily lead to a large $E_{\rm{sym,4}}(\rho_0)$ value of $\approx 20$ MeV obtained previously without considering the high-order surface tension. Furthermore, we also give the expression for the sixth-order symmetry energy $a_{\rm{sym,6}}(A)$ of finite nuclei, which involves more nuclear matter bulk parameters and the higher-order isospin-dependent surface tension.