Viscous relaxation and collective oscillations in a trapped Fermi gas near the unitarity limit

TL;DR

This paper calculates the viscous relaxation time of a trapped Fermi gas near unitarity, analyzing how it influences collective oscillation frequencies and damping, with results relevant to recent experimental observations.

Contribution

It introduces a detailed calculation of viscous relaxation time incorporating energy-dependent scattering, linking microscopic interactions to collective mode behavior.

Findings

Viscous relaxation time varies with temperature and scattering length.

Collective mode frequencies and damping depend on viscous relaxation.

Results align with recent experimental data.

Abstract

The viscous relaxation time of a trapped two-component gas of fermions in its normal phase is calculated as a function of temperature and scattering length, with the collision probability being determined by an energy-dependent s-wave cross section. The result is used for calculating the temperature dependence of the frequency and damping of collective modes studied in recent experiments, starting from the kinetic equation for the fermion distribution function with mean-field effects included in the streaming terms.