Relic abundance explained

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 \equiv (n)/(T ^{3})

where

n is the number density:n \equiv (N)/(V)

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

The relic abundance of a particle is shown by

Y _{infty} indicates the asymptotic value of abundance of a species of a particle which it will reach after its "freeze-out".^[4]

Notes and References

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