universal extra dimensions [@kkdm], and the lightest T-parity odd particle in little Higgs theories [@lh].

Each of these candidates have similar masses and couplings, and thus will undergo similar thermal histories in the early universe. At high temperatures, WIMPs are abundant, being freely created and annihilated in pairs. As the universe expands and the temperature drops below the WIMPs’ production threshold, however, the number density of these particles becomes rapidly suppressed. Ultimately, the WIMPs will “freeze out” and remain as a thermal relic of the universe’s hot youth. The resulting density of WIMPs is given by: \_h\^2 = [s\_0\_c/h\^2]{} ( [45g\_\*]{})\^[1/2]{} [ x\_f m\_]{}[1]{}, where $s_0$ is the current entropy density of the universe, $\rho_c$ is the critical density, $h$ is the (scaled) Hubble constant, $g_*$ is the effective number of relativistic degrees of freedom at the time that the dark matter particle goes out of thermal equilibrium, $m_\Pl$ is the Planck mass, $x_f = m/T_f \approx 25$ is the inverse freeze-out temperature in units of the WIMP mass, and $\VEV{\sigma v}$ is the thermal average of the dark matter pair annihilation cross section times the relative velocity.

In order for this process to yield a thermal abundance of dark 