Bounds on neutrino-scalar nonstandard interactions from big bang nucleosynthesis

TL;DR

This paper uses big bang nucleosynthesis data to set new constraints on neutrino-scalar nonstandard interactions, limiting their effective couplings more stringently than previous studies for certain scalar masses.

Contribution

It provides the first comprehensive bounds on neutrino-scalar interactions from early universe nucleosynthesis, improving existing limits for specific scalar mass ranges.

Findings

$G_{eff} < 1.2$ MeV$^{-2}$ at 68% CL

$G_{S} < 2.0 imes 10^{7}$ MeV$^{-2}$ at 68% CL

Stricter constraints than previous results for $10^{-15}$ eV to $10^{-5}$ eV scalar masses.

Abstract

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 $N_{\rm eff}$. We employ big bang nucleosynthesis to constraint the SNSI effect. We find that $ G_{\rm eff }< 1.2$ MeV$^{-2}$ and $ G_{\rm S }< 2.0 \times 10^{7}$ MeV$^{-2}$ at 68\% CL. For a scalar mass in the range $10^{-15} {\rm eV}\lesssim m_{\phi}\lesssim 10^{-5}{\rm eV}$, our neutrino-scalar coupling constraint is more restrictive than any previous result.