Transport coefficients in superfluid neutron stars

TL;DR

This paper investigates the transport properties like shear and bulk viscosity, and thermal conductivity in superfluid neutron stars, focusing on phonon interactions and their implications for star dynamics.

Contribution

It introduces a systematic approach using effective field theory to compute phonon collision effects on transport coefficients in superfluid neutron star matter.

Findings

Phonon collisions dominate bulk viscosity in neutron star cores.

Thermal conductivity from phonons is temperature-independent.

Comparison shows phonon shear viscosity is lower than electron collision shear viscosity.

Abstract

We study the shear and bulk viscosity coefficients as well as the thermal conductivity as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state and the gap of the system. The shear viscosity due to phonon scattering is compared to calculations of that coming from electron collisions. We also comment on the possible consequences for r-mode damping in superfluid neutron stars. Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars. We finally obtain a temperature-independent thermal conductivity from phonon collisions and compare it with the electron-muon thermal conductivity in superfluid neutron stars.