Elementary excitations in homogeneous neutron star matter

TL;DR

This paper investigates collective density modes in neutron-star matter, focusing on how Coulomb interactions and nuclear forces influence elementary excitations in npe matter between nuclear saturation density and three times that density.

Contribution

It provides a comparative analysis of nuclear interactions using Skyrme forces and microscopic models, highlighting the role of Coulomb effects and nucleon effective mass.

Findings

Coulomb interactions significantly modify proton plasmon modes.

Nucleon effective mass impacts excitation spectra.

Different nuclear force models yield comparable excitation behaviors.

Abstract

We study the collective density modes which can affect neutron-star thermodynamics in the baryonic density range between nuclear saturation ($\rho_0$) and $3\rho_0$. In this region, the expected constituents of neutron-star matter are mainly neutrons, protons and electrons ($npe$ matter), under the constraint of beta equilibrium. The elementary excitations of this $npe$ medium are studied in the RPA framework. We emphasize the effect of Coulomb interaction, in particular the electron screening of the proton plasmon mode. For the treatment of the nuclear interaction, we compare two modern Skyrme forces and a microscopic approach. The importance of the nucleon effective mass is observed.