 Effective number of neutrino species

ID: effective-number-of-neutrino-species

The effective number of neutrino species parametrizes radiation beyond photons through

ρ_{r} = \frac{π ^{2}}{30} [2 + \frac{7}{8} 2 (\frac{4}{11})^{4/3} N_{eff}] T_{γ}^{4} .

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