New constraint on the cosmological background of relativistic particles

Details New constraint on the cosmological background of relativistic particles New constraint on the cosmological background of relativistic particles

2005-10-19

arxiv.org/abs/astro-ph/0510582v2

JCAP 0601:001,2006

Astronomy and Astrophysics

Astrophysics

10 pages, 3 figures, references added

Scientific paper

10.1088/1475-7516/2006/01/001

We have derived new bounds on the relativistic energy density in the Universe from cosmic microwave background (CMB), large scale structure (LSS), and type Ia supernova (SNI-a) observations. In terms of the effective number of neutrino species a bound of N_\nu = 4.2^{+1.2}_{-1.7} is derived at 95% confidence. This bound is significantly stronger than previous determinations, mainly due to inclusion of new CMB and SNI-a observations. The absence of a cosmological neutrino background (N_\nu = 0) is now excluded at 5.4 \sigma. The value of N_\nu is compatible with the value derived from big bang nucleosynthesis considerations, marking one of the most remarkable successes of the standard cosmological model. In terms of the cosmological helium abundance, the CMB, LSS, and SNI-a observations predict a value of 0.240 < Y < 0.281.

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