Collective excitation frequencies and damping rates of a two-dimensional deformed trapped Bose gas above the critical temperature

Abstract

We derive an equation of motion for the velocity fluctuations of a two-dimensional deformed trapped Bose gas just above the critical temperature in the hydrodynamical regime. From this equation, we calculate the eigenfrequencies and the corresponding density fluctuations for a few low-lying excitation modes. Using the method of averages, we derive a dispersion relation in a deformed trap at very high temperature that interpolates between the collisionless and hydrodynamic regimes. We make use of this dispersion relation to calculate the frequencies and the damping rates for monopole and quadrupole mode in both the regimes. We also discuss the time evolution of the wave-packet width of a Bose gas in a time-independent trap as well as a time-dependent trap.