## Cosmic neutrino background |

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The **cosmic neutrino background** (**CNB**, **CνB**^{[1]}) is the universe's background particle radiation composed of **relic neutrinos**.

The CνB is a relic of the

As neutrinos rarely interact with matter, these neutrinos still exist today. They have a very low energy, around 10^{−4} to 10^{−6} ^{[1]} Even high energy neutrinos are ^{−10} times smaller, so the CνB may not be directly observed in detail for many years, if at all.^{[1]} However, Big Bang cosmology makes many predictions about the CνB, and there is very strong indirect evidence that the CνB exists.^{[1]}

- derivation of the cνb temperature
- indirect evidence for the cνb
- prospects for the direct detection of the cνb
- see also
- notes
- references

Given the temperature of the CMB, the temperature of the CνB can be estimated. Before

where *σ* is the entropy, *g* is the effective *T* is the temperature, we find that

where *T*_{0} denotes the temperature before the electron-positron annihilation and *T*_{1} denotes after. The factor *g*_{0} is determined by the particle species:

- 2 for photons, since they are massless
bosons ^{[2]}

- 2 × (7/8) each for electrons and positrons, since they are
fermions .^{[2]}

*g*_{1} is just 2 for photons. So

Given the current value of *T _{γ}* = , 2.725 K

The above discussion is valid for massless neutrinos, which are always relativistic. For neutrinos with a non-zero rest mass, the description in terms of a temperature is no longer appropriate after they become non-relativistic; i.e., when their thermal energy 3/2 *kT _{ν}* falls below the rest mass energy

Other Languages

العربية: خلفية النيوترينو الكونية

català: Fons còsmic de neutrins

čeština: Reliktní neutrina

Deutsch: Kosmischer Neutrinohintergrund

español: Fondo cósmico de neutrinos

فارسی: نوترینوی زمینه کیهانی

français: Fond cosmologique de neutrinos

հայերեն: Մնացորդային նեյտրինային ճառագայթում

日本語: 宇宙ニュートリノ背景

polski: Neutrinowe promieniowanie tła

slovenčina: Kozmické neutrínové pozadie

suomi: Kosminen neutriinotausta

українська: Нейтринне реліктове випромінювання

中文: 宇宙中微子背景輻射