Bounds on neutrino-scalar nonstandard interactions from big bang nucleosynthesis

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, $G_{\mathrm{eff}}$, and the neutrino self-interaction, $G_{\mathrm{S}}$. These parameters are directly related to the effective number of relativistic species and non-zero values imply a smaller than expected $N_{\mathrm{eff}}$. We employ big bang nucleosynthesis to constraint the SNSI effect. We find that $G_{\mathrm{eff}}<1.2$ MeV${}^{-2}$ and $G_{\mathrm{S}}<2.0\times 10^7$ MeV${}^{-2}$ at 68\% CL. For a scalar mass in the range $10^{-15}\mathrm{eV}\lesssim m_{\varphi }\lesssim 10^{-5}\mathrm{eV}$, our neutrino-scalar coupling constraint is more restrictive than any previous result.

Figure added. Improved discussion and computation of the neutrino decoupling due to SNSI. Accepted for publication in PRD