Spin fluctuations, susceptibility and the dipole oscillation of a nearly ferromagnetic Fermi gas

We discuss the spin fluctuations and the role played by the magnetic susceptibility in an atomic Fermi gas interacting with positive scattering length. Both thermal and quantum fluctuations are considered. Using a sum rule approach and recent {\it ab initio} Monte Carlo results for the magnetic susceptibility of uniform matter we provide explicit predictions for the frequency of the spin dipole oscillation of a gas trapped by a harmonic potential and discuss the deviations from the behaviour of an ideal gas when the system approaches the ferromagnetic transition. The role of the Landau's parameters in the characterization of the magnetic properties is also discussed.