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.

Uses

Relic abundance is modelled for WIMPs (weakly interacting massive particles) in the study of dark matter.[1]

Calculation

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

${\displaystyle Y\equiv {\frac {n}{T^{3}}}}$

where ${\displaystyle n}$ is the number density:

${\displaystyle n\equiv {\frac {N}{V}}}$

that is, number of particles per physical volume (not the comoving volume).

The relic abundance of a particle is shown by ${\displaystyle Y_{\infty }}$ indicates the asymptotic value of abundance of a species of a particle which it will reach after its "freeze-out".[4]

References

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