Hydrodynamic damping in trapped Bose gases

Abstract

Griffin, Wu and Stringari have derived the hydrodynamic equations of a trapped dilute Bose gas above the Bose-Einstein transition temperature. We give the extension which includes hydrodynamic damping, following the classic work of Uehling and Uhlenbeck based on the Chapman-Enskog procedure. Our final result is a closed equation for the velocity fluctuations $\delta v$ which includes the hydrodynamic damping due to the shear viscosity $\eta$ and the thermal conductivity $\kappa$. Following Kavoulakis, Pethick and Smith, we introduce a spatial cutoff in our linearized equations when the density is so low that the hydrodynamic description breaks down. Explicit expressions are given for $\eta$ and $\kappa$, which are position-dependent through dependence on the local fugacity when one includes the effect of quantum degeneracy of the trapped gas. We also discuss a trapped Bose-condensed gas, generalizing the work of Zaremba, Griffin and Nikuni to include hydrodynamic damping due to the (non-condensate) normal fluid.

21 pages, revtex, 2 postscript figures. Section IV has been revised. The damping we find is in agreement with the approach used by Kavoulakis, Pethick and Smith (cond-mat/9710130). Submitted to J. Low Temp. Phys