Neutrino non-standard interactions meet precision measurements of Neff

The number of relativistic species, N-eff, has been precisely calculated in the standard model, and would be measured to the percent level by CMB-S4 in future. Neutral-current non-standard interactions would affect neutrino decoupling in the early Universe, thus modifying N-eff. We parameterize those operators up to dimension-7 in the effective field theory framework, and then provide a complete, generic and analytical dictionary for the collision term integrals. From precision measurements of N-eff, the most stringent constraint is obtained for the dimension-6 vector-type neutrino-electron operator, whose scale is constrained to be above about 195 (331) GeV from Planck (CMB-S4). We find our results complementary to other experiments like neutrino coherent scattering, neutrino oscillation, collider, and neutrino deep inelastic scattering experiments.

Automated summary

The study precisely calculates the number of relativistic species, N-eff, in the standard model and predicts it will be measured to the percent level by CMB-S4 in the future. Neutral-current non-standard interactions are found to impact neutrino decoupling in the early Universe, subsequently modifying N-eff. The results provide a comprehensive analysis of the dimension-7 parameterized operators in effective field theory framework and offer a stringent constraint on the dimension-6 vector-type neutrino-electron operator's scale.