Ratio of shear viscosity to entropy density in multifragmentation of Au + Au

TL;DR

This study calculates the shear viscosity to entropy density ratio in Au+Au collisions, revealing a minimum near the nuclear liquid-gas phase transition, with values significantly above the theoretical lower bound.

Contribution

It introduces a quantum molecular dynamics approach to compute the $\\eta/s$ ratio in heavy-ion collisions and links the minimum to the nuclear phase transition.

Findings

The $\\eta/s$ ratio approaches a minimum at higher incident energies.

The minimum $\\eta/s$ value is about 7 times the KSS bound.

The minimum correlates with the nuclear liquid-gas phase transition.

Abstract

The ratio of the shear viscosity ($\eta$) to entropy density ($s$) for the intermediate energy heavy-ion collisions has been calculated by using the Green-Kubo method in the framework of the quantum molecular dynamics model. The theoretical curve of $\eta/s$ as a function of the incident energy for the head-on Au+Au collisions displays that a minimum region of $\eta/s$ has been approached at higher incident energies, where the minimum $\eta/s$ value is about 7 times Kovtun-Son- Starinets (KSS) bound (1/4$\pi$). We argue that the onset of minimum $\eta/s$ region at higher incident energies corresponds to the nuclear liquid gas phase transition in nuclear multifragmentation.