Coannihilation Effects and Relic Abundance of Higgsino-Dominant LSPs
  We calculate the relic abundance of Higgsino-dominant lightest superparticles, taking account of coannihilations with the superparticles which are almost degenerate with the lightest one. We show that their relic abundance is reduced drastically by the coannihilation processes and hence they are cosmologically of no interest. 
Satoshi Mizuta and Masahiro Yamaguchi