Quasiparticle lifetimes in the charged Bose gas and thecuprates

The scattering cross-section of a Coulomb potential screened by a charged Bose gas is calculated both above and below the Bose-Einstein condensation temperature, using the variable-phase method. In contrast with the case for the Bardeen-Cooper-Schrieffer superconductor, the screened scattering potential and quasiparticle lifetime are found to be very different in the superconducting and normal states. We apply the result to explain the appearance of a sharp peak in the angle-resolved photoemission spectra in some cuprates below the superconducting transition.