Shear viscosity of nuclear matter in the spinodal region

Based on Boltzmann-Uehling-Uhlenbeck simulations calibrated by previous efforts of the transport model evaluation project, we have studied the specific shear viscosity q/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 the nuclear phase diagram, we have generated dynamically stable and thermalized nuclear cluster systems in a box with the periodic boundary condition. Extensive results of q/s at different average densities and temperatures in uniform and nonuniform 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 q/s has a minimum only at low average densities of p < 0.3p0. The present study serves as a rigorous baseline calculation of q/s in nuclear systems with clusters, and helps our understanding of the relation between the shear viscosity and the nuclear phase diagram.