Dissipative fluid dynamics for the dilute Fermi gas at unitarity: Free expansion and rotation

TL;DR

This paper studies how shear viscosity affects the expansion and rotation of a dilute Fermi gas at unitarity using dissipative fluid dynamics, highlighting the importance of reheating and the insensitivity to the equation of state.

Contribution

It provides a detailed comparison of numerical solutions and approximations in viscous hydrodynamics for the Fermi gas, emphasizing the role of shear viscosity and reheating effects.

Findings

Shear viscosity causes distinct features in expansion dynamics.

Reheating must be included for accurate modeling.

Expansion mainly constrains the average shear viscosity.

Abstract

We investigate the expansion dynamics of a dilute Fermi gas at unitarity in the context of dissipative fluid dynamics. Our aim is to quantify the effects of shear viscosity on the time evolution of the system. We compare exact numerical solutions of the equations of viscous hydrodynamics to various approximations that have been proposed in the literature. Our main findings are: i) Shear viscosity leads to characteristic features in the expansion dynamics; ii) a quantitative description of these effects has to include reheating; iii) dissipative effects are not sensitive to the equation of state P(n,T) as long as the universal relation P=(2/3)E is satisfied; iv) the expansion dynamics mainly constrains the cloud average of the shear viscosity.