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The Big-Bang Nucleosynthesis Limit to the Number of Neutrino Species

Craig J Copi·David N. Schramm·Michael S. Turner
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Abstract

Concern about systematic uncertainty in the $^4$He abundance as well as the chemical evolution of $^3$He leads us to re-examine this important limit. It is shown that with conservative assumptions no more than the equivalent of 4 massless neutrino species are allowed. Even with the most extreme estimates of the astrophysical uncertainties a meaningful limit still exists, less than 5 massless neutrino species, and illustrates the robustness of this argument. A definitive measurement of the deuterium abundance in high-redshift hydrogen clouds should soon sharpen the limit.

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Craig J Copi, David N. Schramm, Michael S. Turner. 1996-06-10. The Big-Bang Nucleosynthesis Limit to the Number of Neutrino Species. https://doi.org/10.1103/physrevd.55.3389

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