2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/11028Limits 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.To appear in the proceedings of the Texas Symposium on Relativistic Astrophysics held in Chicago, Dec. 15-20 1996. 3 pages, latex, uses included style file sprocl.styAstrophysicstext