1999/01/18 by Allan Griffin, Griffin, Allan
Physics and Astronomy · #Advanced Thermodynamics and Statistical Mechanics #Cold Atom Physics and Bose-Einstein Condensates #Quantum, superfluid, helium dynamics #cond-mat
paper · pdf · doi:10.48550/arxiv.cond-mat/9901172
Lectures given at the BEC Varenna Summer School, July 7-17,1998. To be published in "Bose-Einstein Condensation in Atomic Gases", edited by M.Inguscio, S.Stringari and C. Wieman (Italian Physical Society,1999). PDF figure files are available from the sender
We give an overview of the current theory of collective modes in trapped atomic gases at finite temperatures, when the dynamics of the condensate and non-condensate must both be considered. A simple introduction is given to the quantum field formulation of the dynamics of an interacting Bose-condensed system, based on equations of motion for the condensate wavefunction and single-particle Green's functions for the non-condensate atoms. We discuss the nature of excitations in the mean-field collisionless region, including the Beliaev second-order approximation for the self-energies. We also sketch the derivation of coupled two-fluid hydrodynamic equations using a simple kinetic equation which includes collisions between condensate and non-condensate atoms.