 Late-time relic-neutrino speed

ID: late-time-relic-neutrino-speed

T_{ν} / a ≪ m_{ν}

gives

⟨ v^{2} ⟩^{1/2} ≃ \frac{15 ζ ( 5 )}{ζ ( 3 )} \frac{T _{ν}}{a m _{ν}} .

The thermal speed decreases as

a^{- 1}

after the neutrinos become nonrelativistic.

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