Transport properties and neutrino emissivity of dense neutron-star matter with localized protons

TL;DR

This paper investigates how proton localization in dense neutron star matter affects transport properties and neutrino emission, leading to significant changes in thermal conductivity, viscosity, and cooling processes at high densities.

Contribution

It introduces a model considering proton localization effects on transport coefficients and neutrino emissivity, revealing deviations from standard Fermi liquid behavior in neutron star cores.

Findings

Proton localization decreases thermal, electrical conductivity, and shear viscosity at lower temperatures.

Localized protons suppress conventional neutrino emission processes like modified URCA.

Neutrino bremsstrahlung from electron and neutron scattering off localized protons shows a T^6 dependence.

Abstract

As pointed out by Kutschera and W{\'o}jcik, very low concentration of protons combined with a specific density dependence of effective neutron-proton interaction could lead to a localization of ``proton impurities'' in neutron medium at densities exceeding four times normal nuclear matter density. We study consequences of the localization of protons for transport processes in dense neutron star cores, assuming random distribution of proton impurities. Kinetic equations, relevant for the transport of charge, heat and momentum, are solved using variational method. Localization of protons removes a T^{-2} factor from the transport coefficients, which leads, at lower temperatures, to a strong decrease of thermal conductivity, electrical conductivity and shear viscosity of neutron star matter, as compared to the standard case, where protons form a Fermi liquid. Due to the localization of protons a number of conventional neutrino emission processes (including modified URCA process) become inoperative in neutron star cores. On the other hand, the energy loss rate from neutrino-antineutrino pair bremsstrahlung due to electron and neutron scattering off (localized) protons, will have a specific T^6 dependence, which could modify the cooling of the neutron star core, as compared to the standard case. Possible astrophysical implications of the localization of protons for neutron star evolution and dynamics are discussed.