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Lepton asymmetry and primordial nucleosynthesis in the era of precision cosmology

Pasquale D. Serpico·Georg G. Raffelt
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Abstract

We calculate and display the primordial light-element abundances as a function of a neutrino degeneracy parameter ξcommon to all flavors. It is the only unknown parameter characterizing the thermal medium at the primordial nucleosynthesis epoch. The observed primordial helium abundance Y_p is the most sensitive cosmic ``leptometer.'' Adopting the conservative Y_p error analysis of Olive and Skillman implies -0.04 \alt ξ\alt 0.07 whereas the errors stated by Izotov and Thuan imply ξ=0.0245+-0.0092 (1 sigma). Improved determinations of the baryon abundance have no significant impact on this situation. A determination of Y_p that reliably distinguishes between a vanishing or nonvanishing ξis a crucial test of the cosmological standard assumption that sphaleron effects equilibrate the cosmic lepton and baryon asymmetries.

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Pasquale D. Serpico, Georg G. Raffelt. 2005-06-24. Lepton asymmetry and primordial nucleosynthesis in the era of precision cosmology. https://doi.org/10.1103/physrevd.71.127301

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