The predictions of the light element abundances produced primordially in the standard hot big bang cosmological model with three species of light neutrinos (Nν=3) is consistent with current observational data. If additional species of light neutrinos exist, additional 4He is produced primordially; consistency with observations of 4He leads to an upper bound to Nν which depends on the neutron half-life (τ 1 2), the nucleon-to-photon ratio (or, equivalently, the primordial abundances of deuterium and helium-3) and the primordial mass fraction of 4He (Yp). The bounds to these quantities are reexamined and Nν≤4.0 is reconfirmed.
Bibliographical noteFunding Information:
NSF and the DOE and, at Fermilab their research is supported by NASA.
The research of Gary Steigman is supported at Bartol by the DOE (DE-AC02-78ER-05007), that of K.A.O. is supported at Minnesota also by the DOE (DE-AC02-83ER-40105), at Chicago the research of D.N.S. and M.S.T. is supported by the