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

Based on an improved isospin- and momentum-dependent interaction, I 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)* > m(p)*, 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)* < m(p)*. The effect is larger in nuclear matter at higher densities, lower temperatures, and larger isospin asymmetries, but it does not affect the behavior of the specific shear viscosity much near nuclear liquid-gas phase transition.