Relic abundance

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

1. Kim Griest, "Relic Abundance in More Detail" Archived 2017-01-27 at the Wayback Machine , 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.