Precision calculation of neutrino evolution in the early Universe. (arXiv:2110.11296v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Froustey_J/0/1/0/all/0/1">Julien Froustey</a>
In the primordial Universe, neutrino decoupling occurs only slightly before
electron-positron annihilations. This leads notably to an increased neutrino
energy density compared to the standard instantaneous decoupling approximation,
parametrized by the effective number of neutrino species $N_{rm eff}$. A
precise calculation of neutrino evolution is needed to assess its consequences
during the later cosmological stages, and requires to take into account
multiple effects such as neutrino oscillations, which represents a genuine
numerical challenge. Recently, several key improvements have allowed such a
precise numerical calculation, leading to the new reference value $N_{rm
eff}=3.0440$.
In the primordial Universe, neutrino decoupling occurs only slightly before
electron-positron annihilations. This leads notably to an increased neutrino
energy density compared to the standard instantaneous decoupling approximation,
parametrized by the effective number of neutrino species $N_{rm eff}$. A
precise calculation of neutrino evolution is needed to assess its consequences
during the later cosmological stages, and requires to take into account
multiple effects such as neutrino oscillations, which represents a genuine
numerical challenge. Recently, several key improvements have allowed such a
precise numerical calculation, leading to the new reference value $N_{rm
eff}=3.0440$.
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