Big bang nucleosynthesis limit on N_nu

TL;DR

This paper introduces a simplified method to constrain the number of light particle species during big bang nucleosynthesis, providing bounds on N_nu that help test physics beyond the Standard Model.

Contribution

The authors extend a previous method to include constraints on additional light degrees of freedom, avoiding complex simulations and enabling quick reevaluation with updated abundance data.

Findings

95% confidence bounds on N_nu between 2 and 4

Method allows easy updates with new abundance measurements

Constraints help test theories with extra light particles during nucleosynthesis

Abstract

Recently we presented a simple method for determining the correlated uncertainties of the light element abundances expected from big bang nucleosynthesis, which avoids the need for lengthy Monte Carlo simulations. We now extend this approach to consider departures from the Standard Model, in particular to constrain any new light degrees of freedom present in the thermal plasma during nucleosynthesis. Since the observational situation regarding the inferred primordial abundances has not yet stabilized, we present illustrative 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 technique provided when the abundances are known more accurately.