Relic abundance

Short description: Amount of particles remaining from the Big Bang

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

Y≡nT3

where n is the number density:

n≡NV

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

The relic abundance of a particle is shown by Y∞ indicates the asymptotic value of abundance of a species of a particle which it will reach after its "freeze-out".[4]

## 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. https://books.google.com/books?id=8JJUZoh9YDkC&pg=PA306.
3. ↑ Scott Dodelson (2003). Modern Cosmology. Academic Press. pp. 74–76. ISBN 978-0-12-219141-1. https://books.google.com/books?id=3oPRxdXJexcC&pg=PA74.
4. ↑ Patrick Petter (28 October 2013). Basic Knowledge of Astrophysic: A New Way. epubli. p. 91. ISBN 978-3-8442-7203-1. https://books.google.com/books?id=Ne69AQAAQBAJ&pg=PA91.

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