Specific viscosity of neutron-rich nuclear matter from a relaxation time approach

TL;DR

This paper investigates the specific viscosity of neutron-rich nuclear matter using a relaxation time approach, revealing how it varies with temperature, density, and isospin asymmetry.

Contribution

It introduces a detailed relaxation time model incorporating isospin- and momentum-dependent interactions and experimental nucleon-nucleon cross sections.

Findings

Neutron relaxation time is larger than proton's in neutron-rich matter.

Specific viscosity decreases with temperature due to increased collisions.

At low temperatures, viscosity increases with density; at high temperatures, it slightly decreases.

Abstract

The specific viscosity of neutron-rich nuclear matter is studied from the relaxation time approach using an isospin- and momentum-dependent interaction and the nucleon-nucleon cross sections taken as those from the experimental data modified by the in-medium effective masses as used in the IBUU transport model calculations. The relaxation time of neutrons is larger while that of protons is smaller in neutron-rich nuclear matter compared with that in symmetric nuclear matter, and this leads to a larger specific viscosity in neutron-rich nuclear matter. In addition, the specific viscosity decreases with increasing temperature because of more frequent collisions and weaker Pauli blocking effect at higher temperatures. At lower temperatures the specific viscosity increases with increasing density due to the Pauli blocking effect, while at higher temperatures it slightly decreases with increasing density as a result of smaller in-medium effective masses at higher densities.