Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-06-27
Phys.Rev. D69 (2004) 023509
Astronomy and Astrophysics
Astrophysics
Revised discussion of polarization and reionization history, references updated, results unchanged. Matches the version accept
Scientific paper
10.1103/PhysRevD.69.023509
We consider for the first time the ability of present-day cosmic microwave background (CMB) anisotropies data to determine the primordial helium mass fraction, Y_p. We find that CMB data alone gives the confidence interval 0.160 < Y_p < 0.501 (at 68% c.l.). We analyse the impact on the baryon abundance as measured by CMB and discuss the implications for big bang nucleosynthesis. We identify and discuss correlations between the helium mass fraction and both the redshift of reionization and the spectral index. We forecast the precision of future CMB observations, and find that Planck alone will measure Y_p with error-bars of 5%. We point out that the uncertainty in the determination of the helium fraction will have to be taken into account in order to correctly estimate the baryon density from Planck-quality CMB data.
Hansen Steen H.
Trotta Roberto
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