In cosmology, the relic abundance of a given elementary particle is a measure of the present quantity of that particle remaining from the Big Bang.
Relic abundance is modelled for WIMPs (weakly interacting massive particles) in the study of dark matter.[1]
Assuming that an elementary particle was formerly in thermal equilibrium, its relic abundance may be calculated using a Boltzmann equation.[2]
The temperature scaled abundance of a particle is defined[3] by
where is the number density:
that is, number of particles per physical volume (not the comoving volume).
The relic abundance of a particle is shown by indicates the asymptotic value of abundance of a species of a particle which it will reach after its "freeze-out".[4]