  Accepting the fine tuned cosmological constant hypothesis, we have recently
proposed that this hypothesis can be tested if the dark matter freeze out
occurs at the electroweak scale and if one were to measure an anomalous shift
in the dark matter relic abundance. In this paper, we numerically compute this
relic abundance shift in the context of explicit singlet extensions of the
Standard Model and explore the properties of the phase transition which would
lead to the observationally most favorable scenario. Through the numerical
exploration, we explicitly identify a parameter space in a singlet extension of
the standard model which gives order unity observable effects. We also clarify
the notion of a temperature dependence in the vacuum energy.
