Gaugino and Higgsino Coannihilations I: Neutralino-Neutralino   Interactions
  We present exact analytic cross sections for all neutralino-neutralino coannihilations into two-body tree level final states. These expressions allow the calculation of important contributions to the neutralino relic abundance over large regions of mSUGRA parameter space and are particularly useful in theories with non-universal gaugino masses. 
A. Birkedal-Hansen and E. Jeong