2001/05/14 by Steen Hannestad · 1 citation
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Cosmology and Gravitation Theories #Radio Astronomy Observations and Technology #astro-ph #hep-ph
paper · pdf · doi:10.1103/physrevd.64.083002
published as Phys.Rev. D64 (2001) 083002 · 5 pages, 3 figures
arxiv created 2001/05/14 · openalex publication_date 2001/09/04 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
New precision cosmic microwave background radiation (CMBR) anisotropy data are beginning to constrain physics beyond the standard model, for example, in the form of additional light particle species. These constraints are complementary to what can be obtained from big bang nucleosynthesis considerations because they apply to much later times. We derive a constraint on the equivalent number of neutrino species, N_\ensuremathν, from the presently available data. Specifically we analyze two different CMBR data sets to test the robustness of our results. Analyzing only CMBR data yields an upper bound of N_\ensuremathν\ensuremath\lesssim17 (95% confidence). Adding large scale structure (LSS) data from the PSC-z survey tightens the upper bound slightly. However, the addition of LSS data gives a nontrivial lower bound of N_\ensuremathν>~1.5/2.5 (95% confidence) for the two data sets. This is the first independent indication of the presence of the cosmological neutrino background which is predicted by the standard model, and seen in big bang nucleosynthesis. The value N_\ensuremathν=0 is disfavored at 3\ensuremathσ and 4\ensuremathσ for the two data sets respectively.