Bounds on neutrino-scalar nonstandard interactions from big bang nucleosynthesis

Understand

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/positrons, $G_{\rm eff}$, and the neutrino self-interaction, $G_{\rm S}$.
• These parameters are directly related to the effective number of relativistic species and non-zero values imply a smaller than expected $N_{\rm eff}$.