Coherent forward scattering processes by neutrino-scalar nonstandard interactions (SNSI) induce an effective neutrino mass. In the early Universe, a large neutrino effective mass restricts the production of neutrinos. The SNSI effect is modulated by two effective couplings; these account for the coupling between neutrinos and electrons or positrons, G eff , and the neutrino self-interaction G S . These parameters are directly related to the effective number of relativistic species, and nonzero values imply a smaller than expected N eff . We employ big bang nucleosynthesis to constraint the SNSI effect. We find that G eff < 1.2 ? ? MeV ? 2 and G S < 2.0 × 10 7 ? ? MeV ? 2 at 68%?C.L. For a scalar mass in the range 10 ? 15 ? ? eV ? m ? ? 10 ? 5 ? ? eV , our neutrino-scalar coupling constraint is more restrictive than any previous result.
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