Dark Matter Annihilations in the Causal Diamond
  We investigate the implications of dark matter annihilations for cosmological
parameter constraints using the causal entropic principle. In this approach
cosmologies are weighted by the total entropy production within a causally
connected region of spacetime. We calculate the expected entropy from dark
matter annihilations within the causal diamond and investigate the preferred
values of the cosmological constant and the mass and annihilation cross section
of the annihilating dark matter and their dependence on the assumptions in the
models. For realistic values of the cross section we typically find preferred
values of $\Lambda $ on the order of $10^{-5}$ of the present value assuming
dark matter annihilations are the primary source of entropy production. The
greatest amount of entropy production from dark matter within the causal
diamond is likely to occur with light keV scale dark matter with low
annihilation cross section. We also investigate the effect of combining this
entropy with the entropy production from stars, and show that if the primary
source of entropy production is from stars, varying the dark matter cross
section directly produces a preferred value of $\Omega_m$ in excellent
agreement with observations.
