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arXiv · 2110.11296

Precision calculation of neutrino evolution in the early Universe

Julien Froustey
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Abstract

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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Julien Froustey. 2021-10-21. Precision calculation of neutrino evolution in the early Universe. https://doi.org/10.1088/1742-6596/2156/1/012013

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