Probing the Effective Number of Neutrino Species with Cosmic Microwave Background

Ichikawa, Kazuhide; Sekiguchi, Toyokazu; Takahashi, Tomo

Probing the Effective Number of Neutrino Species with Cosmic Microwave Background

Authors

Ichikawa, Kazuhide

Sekiguchi, Toyokazu

Takahashi, Tomo

Description

We discuss how much we can probe the effective number of neutrino species N_nu with cosmic microwave background alone. Using the data of WMAP, ACBAR, CBI and BOOMERANG experiments, we obtain a constraint on the effective number of neutrino species as 0.96< N_nu <7.94 at 95% C.L. for a power-law LCDM flat universe model. The limit is improved to be 1.39 < N_nu < 6.38 at 95% C.L. if we assume that the baryon density, N_nu 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 N_nu, we investigate how the big bang nucleosynthesis relation affects the estimation for these parameters and other cosmological parameters.
19 pages, 4 figures, 4 tables; update after WMAP 5-year results; accepted for publication in Phys. Rev. D