Phys. Rev. D 78, 083526 (2008) [10 pages]Probing the effective number of neutrino species with the cosmic microwave backgroundReceived 31 July 2008; published 16 October 2008 We discuss how much we can probe the effective number of neutrino species Nν with the cosmic microwave background alone. Using the data of the WMAP, ACBAR, CBI, and BOOMERANG experiments, we obtain a constraint on the effective number of neutrino species as 0.96<Nν<7.94 at 95% C.L. for a power-law ΛCDM flat universe model. The limit is improved to be 1.39<Nν<6.38 at 95% C.L. if we assume that the baryon density, Nν, and the helium abundance are related by the big bang nucleosynthesis theory. We also provide a forecast for the Planck experiment using a Markov chain Monte Carlo approach. In addition to constraining Nν, we investigate how the big bang nucleosynthesis relation affects the estimation for these parameters and other cosmological parameters. © 2008 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevD.78.083526
DOI:
10.1103/PhysRevD.78.083526
PACS:
98.80.−k, 26.35.+c, 98.70.Vc
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