= Boltzmann suppression of a nonrelativistic relic
{c}
{title2=$n_{\rm eq}\simeq g(mT/2\pi)^{3/2}e^{-m/T}$}
A nonrelativistic species with $g$ states and negligible <chemical potential> has equilibrium density $g(mT/(2\pi))^{3/2}e^{-m/T}$. If particle-antiparticle annihilation maintains equilibrium after the species becomes massive, its eventual freeze-out population can be much smaller than a relativistically decoupled population. The nonrelativistic annihilation rate and any asymmetry determine the final abundance.
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