Big bang nucleosynthesis limit on N-nu - art. no. 123520.

Recently we presented a simple method for determining the correlated uncert ainties of the light element abundances expected from big bang nucleosynthe sis, which avoids the need for lengthy Monte Carlo simulations. We now exte nd this approach to consider departures from the standard model, in particu lar to constrain any new light degrees of freedom present in the thermal pl asma during nucleosynthesis. Since the observational situation regarding th e inferred primordial abundances has not yet stabilized, we present illustr ative bounds on the equivalent number of neutrino species N-nu for various combinations of individual abundance determinations. Our 95% C.L. bounds on N-nu range between 2 and 4, and can easily be reevaluated using the techni que provided when the abundances are known more accurately. [S0556-2821(99) 04412-4].