QCD Equation of State and Dark Matter

The relic density of weakly interacting massive particles (WIMPs) depends on the entropy and the expansion rate of the Universe when they freeze out, at a temperature in the range 100 MeV - 10GeV. We use recent calculations of the QCD pressure to produce a new equation of state suitable for use in relic density calculations. We show that relic densities calculated by the dark matter package DarkSUSY receive corrections of several %, within the observational accuracy of current (WMAP) and future (Planck) CMB missions.