Transport coefficients of two-flavor superconducting quark matter

TL;DR

This paper calculates the electrical, thermal conductivities, and shear viscosity of two-flavor color superconducting quark matter, providing insights into its transport properties relevant for neutron star observations.

Contribution

It offers the first detailed calculation of transport coefficients in 2SC quark matter using a variational approach with weak coupling expansion.

Findings

Transport coefficients scale with temperature and chemical potential.

Fermion scattering by flux tubes is negligible for thermal conductivity.

Flux tubes may affect electrical conductivity and shear viscosity at low temperatures or high magnetic fields.

Abstract

Background: The two-flavor color superconducting (2SC) phase of quark matter is a possible constituent of the core of neutron stars. To assess its impact on the observable behavior of the star one must analyze transport properties, which in 2SC matter are controlled by the scattering of gapless fermionic modes by each other and possibly also by color-magnetic flux tubes. Purpose: We determine the electrical and thermal conductivities and the shear viscosity of 2SC matter. Methods: We use a variational formulation of transport theory, treating the strong and electromagnetic interactions via a weak coupling expansion. Results: We provide the leading order scaling of the transport coefficients with temperature and chemical potential as well as accurate fits to our numerical results. We also find that the scattering of fermions by color-magnetic flux tubes is insignificant for thermal conductivity, but may contribute to the electrical conductivity and shear viscosity in the limit of very low temperature or high magnetic field. We also estimate the transport coefficients in unpaired quark matter. Conclusions: Our calculation has set the stage for exploration of possible signatures of the presence of 2SC quark matter in neutron stars.