Widths of Giant Resonances

Theories of giant resonances are reviewed. The Green's functions and response functions are introduced in connection with inelastic scattering cross sections exciting giant resonances. The Green's function is calculated in terms of the effective Hamiltonian in a truncated bound configuration space, and the escape and spreading widths appear as the decay probability to the continuum space and more complicated states. A few examples of existing calculations are reviewed, their methods of the calculations are examined and the results are compared with each other.