@article{chafin_schaefer_2013, title={Hydrodynamic fluctuations and the minimum shear viscosity of the dilute Fermi gas at unitarity}, volume={87}, ISSN={["1094-1622"]}, url={http://inspirehep.net/record/1184528}, DOI={10.1103/physreva.87.023629}, abstractNote={We study hydrodynamic fluctuations in a non-relativistic fluid. We show that in three dimensions fluctuations lead to a minimum in the shear viscosity to entropy density ratio $\eta/s$ as a function of the temperature. The minimum provides a bound on $\eta/s$ which is independent of the conjectured bound in string theory, $\eta/s \geq \hbar/(4\pi k_B)$, where $s$ is the entropy density. For the dilute Fermi gas at unitarity we find $\eta/s\gsim 0.2\hbar$. This bound is not universal -- it depends on thermodynamic properties of the unitary Fermi gas, and on empirical information about the range of validity of hydrodynamics. We also find that the viscous relaxation time of a hydrodynamic mode with frequency $\omega$ diverges as $1/\sqrt{\omega}$, and that the shear viscosity in two dimensions diverges as $\log(1/ \omega)$.}, number={2}, journal={PHYSICAL REVIEW A}, author={Chafin, Clifford and Schaefer, Thomas}, year={2013}, month={Feb} }
 @article{chafin_schaefer_2013, title={Scale breaking and fluid dynamics in a dilute two-dimensional Fermi gas}, volume={88}, ISSN={["1094-1622"]}, url={http://inspirehep.net/record/1247297}, DOI={10.1103/physreva.88.043636}, abstractNote={We study two observables related to the anomalous breaking of scale invariance in a dilute two dimensional Fermi gas, the frequency shift and damping rate of the monopole mode in a harmonic confinement potential. For this purpose we compute the speed of sound and the bulk viscosity of the two dimensional gas in the high temperature limit. We show that the anomaly in the speed of sound scales as $(2P-\rho c_s^2)/P\sim z/[\log(T/E_B)]^2$, and that the bulk viscosity $\zeta$ scales as $\zeta/\eta \sim z^2/[\log(T/E_B)]^6$. Here, $P$ is the pressure, $c_s^2$ is the speed of sound, $\eta$ is the shear viscosity, $z$ is the fugacity, and $E_B$ is the two-body binding energy. We show that our results are consistent with the experimental results of Vogt et al. [Phys. Rev. Lett. 108, 070404 (2012)]. Vogt et al. reported a frequency shift $\delta\omega/\omega$ of the order of a few percent, and a damping rate smaller than the background rate $\Gamma/\omega_0\sim 5%$.}, number={4}, journal={PHYSICAL REVIEW A}, author={Chafin, Clifford and Schaefer, Thomas}, year={2013}, month={Oct} }