Neutrino Physics and the Primordial Elemental Abundances

Limits can be placed on nonstandard neutrino physics when big bang nucleosynthesis (BBN) calculations employing standard neutrino physics agree with the observationally inferred primordial abundances of deuterium (D), ${}^3$He, ${}^4$He, and ${}^7$Li. These constraints depend most sensitively on the abundances of D and ${}^4$He. New observational determinations of the primordial D and/or ${}^4$He abundances could force revisions in BBN constraints on nonstandard neutrino physics.