Transport coefficients of hyperonic neutron star cores

TL;DR

This paper calculates the transport properties of hyperonic matter in neutron star cores, revealing neutron dominance in thermal conductivity and shear viscosity, especially at high densities due to hyperon effects.

Contribution

It provides the first detailed calculations of thermal conductivity and shear viscosity in hyperonic neutron star matter using Brueckner-Hartree-Fock interactions.

Findings

Neutrons dominate thermal conductivity across densities.

Hyperons cause neutrons to dominate shear viscosity at high densities.

Transport coefficients are significantly affected by hyperon presence.

Abstract

We consider transport properties of the hypernuclear matter in neutron star cores. In particular, we calculate the thermal conductivity, the shear viscosity, and the momentum transfer rates for np$\Sigma^{-}\Lambda e\mu$ composition of dense matter in $\beta$--equilibrium for baryon number densities in the range $0.1-1$~fm$^{-3}$. The calculations are based on baryon interactions treated within the framework of the non-relativistic Brueckner-Hartree-Fock theory. Bare nucleon-nucleon (NN) interactions are described by the Argonne v18 phenomenological potential supplemented with the Urbana IX three-nucleon force. Nucleon-hyperon (NY) and hyperon-hyperon (YY) interactions are based on the \new{NSC97e and NSC97a models} of the Nijmegen group. We find that the baryon contribution to transport coefficients is dominated by the neutron one as in the case of neutron star cores containing only nucleons. In particular, we find that neutrons dominate the total thermal conductivity over the whole range of densities explored and that, due to the onset of $\Sigma^-$ which leads to the deleptonization of the neutron star core, they dominate also the shear viscosity in the high density region, in contrast with the pure nucleonic case where the lepton contribution is always the dominant one.