Theory of giant resonances

A review is given of the present status of the theory of giant resonances in cold nuclei. We first focus on a macroscopic description in terms of viscous hydrodynamics and sum rules which historically have played a substantial role in the interpretation of giant resonances as highly collective modes. Based on mean field theory a fluid dynamical treatment is discussed emphasizing the ''zero sound'' nature of giant resonances. The close analogy to Landau's theory of normal Fermi liquids is stressed. Special attention is paid to various damping processes (Landau damping, collisional damping) which characterize the decay of giant resonances. Within the mean field picture we then give a detailed, purely microscopic description provided by the RPA and extended versions which include coupling to more complex states. Theoretical results are presented and compared with experiments. (author). 174 refs, figs and tabs