## 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 ^{4}He and ^{7}Li. 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 ^{4}He abundances Y_{p} = 0.225-0.250, as well as a range in primordial ^{7}Li abundances from (1.6 to 4.1) × 10^{-10}. For (^{7}Li/H)_{p} = 1.6 × 10^{-10}, as can be inferred from the ^{7}Li data from Population II halo stars, the upper limit to N_{p} based on the current best estimate of the primordial ^{4}He abundance of Y_{p} = 0.238 is N_{ν} < 4.3 and varies from N_{ν} < 3.3 (at 95% C.L.) when Y_{p} = 0.225 to N_{ν} < 5.3 when Y_{p} = 0.250. If ^{7}Li is depleted in these stars the upper limit to N_{ν} is relaxed. Taking (^{7}Li/H)_{p} = 4.1 × 10^{-10}, the limit varies from N_{ν} < 3.9 when Y_{p} = 0.225 to N_{ν} ≲ 6 when Y_{p} = 0.250. We also consider the consequences on the upper limit to N_{ν} if recent observations of deuterium in high-redshift quasar absorption-line systems are confirmed.

Original language | English (US) |
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Pages (from-to) | 403-411 |

Number of pages | 9 |

Journal | Astroparticle Physics |

Volume | 11 |

Issue number | 4 |

DOIs | |

State | Published - Sep 1999 |

### Bibliographical note

Funding Information:We note that this work was begun in collaboration with David Schramm.T his work was supportedi n part by DOE grant DE-FG02-94ER40823 at Minnesota.