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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.

Calculation

Assuming that an elementary particle was formerly in thermal equilibrium, its relic abundance may be calculated using a Boltzmann equation.

The temperature scaled abundance of a particle is defined 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".

References

1. Kim Griest, "Relic Abundance in More Detail", The Net Advance of Physics: The Nature of Dark Matter, Section 6C, MIT
2. J. Thanh Van Tran (1 January 1990). Z0 Physics: Proceedings of the XXVth Rencontre de Moriond, Les Arcs, Savoie, France, March 4-11, 1990. Atlantica Séguier Frontières. p. 306. ISBN 978-2-86332-081-5.
3. Scott Dodelson (2003). Modern Cosmology. Academic Press. pp. 74–76. ISBN 978-0-12-219141-1.
4. Patrick Petter (28 October 2013). Basic Knowledge of Astrophysic: A New Way. epubli. p. 91. ISBN 978-3-8442-7203-1.

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