New constraint on the cosmological background of relativistic particles

Abstract

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_ν= 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_ν= 0) is now excluded at 5.4 σ. The value of N_νis 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.

10 pages, 3 figures, references added

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• Cosmology of neutrinos and extra light particles after WMAP3
• The Imprint of Relativistic Particles on the Anisotropies of the Stochastic Gravitational-Wave Background
• Gauge Trimming of Neutrino Masses
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• Sterile neutrinos: direct mixing effects versus induced mass matrix of active neutrinos
• Constraint on the Effective Number of Neutrino Species from the WMAP and SDSS LRG Power Spectra
• Probing neutrino oscillations from supernovae shock waves via the IceCube detector
• Probing the Effective Number of Neutrino Species with Cosmic Microwave Background
• Constraining neutrino masses with the ISW-galaxy correlation function
• Relaxed constraints on neutrino oscillation parameters
• Mass limits for heavy neutrinos