Collective oscillations of an interacting trapped Fermi gas

We calculate the effects of two-body interactions on the low frequency oscillations of a normal Fermi gas confined in a harmonic trap. The mean field contribution to the collective frequencies is evaluated in the collisionless regime using a sum rule approach. We also discuss the transition between the collisionless and hydrodynamic regime with special emphasis to the spin dipole mode in which two atomic clouds occupying different spin states oscillate in opposite phase. The spin dipole mode is predicted to be overdamped in the hydrodynamic regime. The relaxation time is calculated as a function of temperature and the effects of Fermi statistics are explicitly pointed out.