Shear viscosity of nuclear matter in the spinodal region

TL;DR

This study uses transport simulations and the Green-Kubo method to analyze the shear viscosity of nuclear matter in the spinodal region, revealing its dependence on density, temperature, and clustering effects.

Contribution

It provides the first systematic calculation of shear viscosity in nuclear matter with clusters, linking viscosity behavior to the nuclear phase diagram.

Findings

Shear viscosity is lower in systems with nuclear clusters due to enhanced correlations.

The temperature dependence of shear viscosity shows a minimum at low densities.

Shear viscosity behavior varies with density and temperature, especially in the spinodal region.

Abstract

Based on IBUU simulations calibrated by previous efforts of the transport model evaluation project, we have studied the specific shear viscosity $\eta/s$ of nuclear matter in the spinodal region using the Green-Kubo method. With the momentum-independent mean-field potential which reproduces reasonably well empirical nuclear matter properties and nuclear phase diagram, we have generated dynamically stable and thermalized nuclear cluster systems in a box with the periodic boundary condition. Extensive results of the $\eta/s$ at different average densities and temperatures in uniform and non-uniform systems are compared, and we found that the shear viscosity is smaller with nuclear clusters due to the enhanced correlation of the energy-momentum tensor and the stronger collision effect. The temperature dependence of the $\eta/s$ has a minimum only at low average densities of $\rho<0.3\rho_0$. The present study serves as a rigorous baseline calculation of the $\eta/s$ in nuclear systems with clusters, and helps to understand the relation between the shear viscosity and the nuclear phase diagram.