Implications of hydrodynamic fluctuations on the minimum shear viscosity of the dilute Fermi gas at unitarity

TL;DR

This paper investigates how hydrodynamic fluctuations influence the minimum shear viscosity in the dilute Fermi gas at unitarity, deriving bounds and analyzing data to reconcile previous discrepancies near the critical temperature.

Contribution

It derives lower bounds for shear viscosity to entropy density ratios using experimental and Monte Carlo data, expanding understanding of viscosity limits in strongly interacting Fermi gases.

Findings

Derived bounds for ta/n and ta/s as functions of temperature.

Re-analyzed quantum Monte Carlo data to address discrepancies in viscosity measurements.

Suggested a possible resolution for the tension between different viscosity bounds.

Abstract

We confirm and expand on work by Chafin and Schaefer on hydrodynamic fluctuations in the unitary Fermi gas. Using the result for the equation of state from a recent MIT experiment, we derive lower bounds for \eta/n and \eta/s as a function of temperature. Re-analyzing recent quantum Monte Carlo data for the shear-viscosity spectral function we point out a possible resolution for the tension between the viscosity bound \eta/n> 0.3 from Chafin and Schaefer and the quantum Monte Carlo results \eta/n<0.2$ from Wlazlowski et al. near the critical temperature