Abstract
Within a relaxation time approach using free nucleon–nucleon cross sections modified by the in-medium nucleon masses that are determined from an isospin- and momentum-dependent effective nucleon–nucleon interaction, we investigate the specific shear viscosity (η/s) of neutron-rich nucleonic matter near its liquid–gas phase transition. It is found that as the nucleonic matter is heated at fixed pressure or compressed at fixed temperature, its specific shear viscosity shows a valley shape in the temperature or density dependence, with the minimum located at the boundary of the phase transition. Moreover, the value of η/s drops suddenly at the first-order liquid–gas phase transition temperature, reaching as low as 4–5 times the KSS bound of ℏ/4π. However, it varies smoothly for the second-order liquid–gas phase transition. Effects of the isospin degree of freedom and the nuclear symmetry energy on the value of η/s are also discussed.
Highlights
Transport properties of hot nuclear matter at various densities, such as the shear viscosity, can be extracted from model analyses of heavy-ion collisions
The specific shear viscosity shows a minimum value around the critical temperature of the hadron-quark phase transition [6, 7]. It is argued in Ref. [6] that the existence of a minimum in the specific shear viscosity is due to the difficulty for the momentum transport in the QGP as its temperature is close to the critical temperature
It has been shown that the boundaries of both mechanical and chemical instabilities responsible for the phase separation [24, 25] and the phase coexistence line [26, 27] in asymmetric nucleonic matter depend on the value of the nuclear symmetry energy Esym(ρ) at subsaturation densities
Summary
Transport properties of hot nuclear matter at various densities, such as the shear viscosity, can be extracted from model analyses of heavy-ion collisions. Is the valley shape structure in the temperature and density dependence of the specific shear viscosity of nucleonic matter the result of the liquid-gas phase transition?
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