Implications of mixed axion/neutralino dark matter for the Cosmic
  Frontier: a Snowmass whitepaper
  If one simultaneously invokes the SUSY solution to the gauge hierarchy
problem and the PQ solution to the strong CP problem, then one might expect
mixed axion/neutralino dark matter (DM), i.e. two dark matter particles. In
this case, dark matter production involves oscillation production of axions,
thermal and non-thermal neutralino production and thermal and non-thermal
production of axinos and saxions. The latter particles may feed additional
neutralinos into the cosmic soup, or dilute all relics via additional entropy
production, or feed dark radiation into the cosmos. Depending on the SUSY and
PQ model, the PQ scale can easily exist from 10^9-10^{16} GeV. Axions may lie
well beyond the range currently being probed by experiment. In the case of
relic WIMPs, theoretical predictions must be rescaled for the possibility that
WIMPs only comprise a fraction of the local DM abundance.
