Single-particle spectrum of the degenerate electron gas

The single-particle spectrum of an interacting electron gas is discussed. There is a characteristic structure in the spectral weight function at energies that differ from the quasi-particle energy by energies of the order of the plasma energy. This structure is due to the singular Coulomb potential and the plasmon part of the effective interaction at long wavelengths. For momenta deep inside the Fermi sea a new elementary excitation of appreciable strength appears. It can be interpreted as a coupled mode of holes and plasmons.