Lepton asymmetry and primordial nucleosynthesis in the era of precision cosmology

Details Lepton asymmetry and primordial nucleosynthesis in the era of precision cosmology Lepton asymmetry and primordial nucleosynthesis in the era of precision cosmology

2005-06-08

arxiv.org/abs/astro-ph/0506162v2

Phys.Rev. D71 (2005) 127301

Astronomy and Astrophysics

Astrophysics

5 pages, 2 figures; minor changes, references added, replaced to match the published version in PRD (Brief Reports)

Scientific paper

10.1103/PhysRevD.71.127301

We calculate and display the primordial light-element abundances as a function of a neutrino degeneracy parameter \xi common 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 \xi \alt 0.07 whereas the errors stated by Izotov and Thuan imply \xi=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 \xi is a crucial test of the cosmological standard assumption that sphaleron effects equilibrate the cosmic lepton and baryon asymmetries.

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