Isospin splitting of nucleon effective mass and shear viscosity of nuclear matter

TL;DR

This paper investigates how the isospin splitting of nucleon effective mass influences the shear viscosity of neutron-rich nuclear matter, revealing that mass differences significantly affect viscosity, especially at high densities and asymmetries.

Contribution

It introduces an improved isospin- and momentum-dependent interaction model to analyze the impact of nucleon effective mass splitting on shear viscosity.

Findings

Neutron effective mass greater than proton mass results in smaller neutron relaxation time.

Shear viscosity is reduced in neutron-rich matter with neutron effective mass larger than proton's.

Effect of mass splitting is more pronounced at higher densities, lower temperatures, and larger isospin asymmetries.

Abstract

Based on an improved isospin- and momentum-dependent interaction, we have studied the qualitative effect of isospin splitting of nucleon effective mass on the specific shear viscosity of neutron-rich nuclear matter from a relaxation time approach. It is seen that for $m_n^\star>m_p^\star$, the relaxation time of neutrons is smaller and the neutron flux between flow layers is weaker, leading to a smaller specific shear viscosity of neutron-rich matter compared to the case for $m_n^\star<m_p^\star$. The effect is larger in nuclear matter at higher densities, lower temperatures, and larger isospin asymmetries, but it doesn't affect much the behavior of the specific shear viscosity near nuclear liquid-gas phase transition.