Collective oscillations of an interacting trapped Fermi gas

We calculate the effects of two-body interactions on the low-frequency osci llations of a normal Fermi gas confined in a harmonic trap. The mean-field contribution to the collective frequencies is evaluated in the collisionles s regime using a sum-rule approach. We also discuss the transition between the collisionless and hydrodynamic regimes with special emphasis on the spi n dipole mode in which two atomic clouds occupying different spin states os cillate in the opposite phase. The spin dipole mode is predicted to be over damped in the hydrodynamic regime. The relaxation time is calculated as a f unction of temperature and the effects of Fermi statistics are explicitly p ointed out. [S1050-2947(99)01212-3].