Auger decay of degenerate and Bose-condensed excitons in Cu$_2$O
  We study the non-radiative Auger decay of excitons in Cu$_2$O, in which two excitons scatter to an excited electron and hole. The exciton decay rate for the direct and the phonon-assisted processes is calculated from first principles; incorporating the band structure of the material leads to a relatively shorter lifetime of the triplet state ortho excitons. We compare our results with the Auger decay rate extracted from data on highly degenerate triplet excitons and Bose-condensed singlet excitons in Cu$_2$O. 
G.M. Kavoulakis (Physics Department, University of Illinois, Urbana)   and Gordon Baym