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Generalized limits to the number of light particle degrees of freedom from big bang nucleosynthesis |
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| Authors: | Keith A Olive David Thomas |
| Institution: | a University of Minnesota, School of Physics and Astronomy Theoretical Physics Institute, 116 Church St SE, Minneapolis, MN 55455, USA b University of Chicago, Astronomy & Astrophysics Center, 5640 S Ellis Ave, Chicago, IL 60637, USA |
| Abstract: | We compute the big bang nucleosynthesis limit on the number of light neutrino degrees of freedom in a model-independent likelihood analysis based on the abundances of 4He and 7Li. We use the two-dimensional likelihood functions to simultaneously constrain the baryon-to-photon ratio and the number of light neutrinos for a range of 4He abundances Yp = 0.225–0.250, as well as a range in primordial 7Li abundances from (1.6 to 4.1) ×10−10. For (7Li/H)p = 1.6 × 10−10, as can be inferred from the 7Li data from Population II halo stars, the upper limit to Nν based on the current best estimate of the primordial 4He abundance of Yp = 0.238 is Nν < 4.3 and varies from Nν < 3.3 (at 95% C.L.) when Yp = 0.225 to Nν < 5.3 when Yp = 0.250. If 7Li is depleted in these stars the upper limit to Nν is relaxed. Taking (7Li/H)p = 4.1 × 10−10, the limit varies from Nν < 3.9 when Yp = 0.225 to Nν  6 when Yp = 0.250. We also consider the consequences on the upper limit to Nν if recent observations of deuterium in high-redshift quasar absorption-line systems are confirmed. |
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