Impact of non-standard neutrino-electron interactions on Big Bang Nucleosynthesis

Abstract

Neutrino non-standard interactions (NSI) with electrons, predicted in many extended theoretical models of particle physics, are known to alter the picture of neutrino decoupling from the cosmic plasma. We update previous analyses of neutrino decoupling in presence of NSI with electrons, extending the parameter space in order to provide, for the first time, a full study of their effect on the production of light elements during Big Bang Nucleosynthesis (BBN). We compare the BBN bounds on non-universal and flavour-changing NSI parameters with the constraints from terrestrial experiments. Our results show that the limits from BBN are significantly less stringent than the experimental bounds, but they are complementary and can provide a test of neutrino physics at different temperature scales and epochs.

Figures (6)

• Figure 1: Values of $N_{\rm eff}$ as a function of non-universal NSI parameters, $\varepsilon^L_{\alpha\alpha}$ in the left panel and $\varepsilon^R_{\alpha\alpha}$ in the right panel, for $\alpha = \{e,\tau\}$. The dashed line corresponds to the standard prediction $N_{\rm eff} = 3.044$, and the shaded region corresponds to $\pm0.02$, which is the expected 1$\sigma$ uncertainty from future cosmological observations Ade:2018sbj. The shaded vertical bands correspond to the 90% C.L. bounds shown in Table \ref{['tab:NSIbounds']}, in orange for the $\tau\tau$ coupling and in blue for the $ee$ ones.
• Figure 2: Values of $N_{\rm eff}$ as a function of two diagonal NSI parameters. Left panel: $\varepsilon^L_{ee}$ - $\varepsilon^R_{ee}$; right panel: $\varepsilon^L_{ee}$ - $\varepsilon^L_{\tau\tau}$. White-shaded regions correspond to the 90% C.L. experimental bounds obtained varying one parameter at a time (Table \ref{['tab:NSIbounds']}).
• Figure 3: Primordial abundances of helium-4 (mass fraction) and deuterium (number density normalised to hydrogen) as functions of the NSI parameters: non-universal left-handed $\varepsilon_{ee}^{L}$ and $\varepsilon_{\tau\tau}^{L}$ (top panel), non-universal right-handed $\varepsilon_{ee}^{R}$ and $\varepsilon_{\tau\tau}^{R}$ (middle panel), and left-handed flavour-changing coupling $\varepsilon_{e\tau}^{L}$ (bottom panel). The shaded grey regions correspond to the observational best fit $1\sigma$ bounds (Table \ref{['tab:primordial_abundances']}). The shaded red region in the right panel corresponds to the old (2024) recommended observation $1\sigma$ bounds for deuterium, see the main text for details. The shaded vertical bands correspond to the 90% C.L. bounds shown in Table \ref{['tab:NSIbounds']}.
• Figure 4: Values of $Y_p$ when varying two diagonal NSI parameters simultaneously. Top left panel: $\varepsilon^L_{ee}$ - $\varepsilon^R_{ee}$; top right panel: $\varepsilon^L_{\tau\tau}$ - $\varepsilon^R_{\tau\tau}$; bottom left panel: $\varepsilon^L_{ee}$ - $\varepsilon^L_{\tau\tau}$; bottom right panel: $\varepsilon^R_{ee}$ - $\varepsilon^R_{\tau\tau}$. White-shaded regions correspond to the 90% C.L. experimental bounds obtained varying one parameter at a time (Table \ref{['tab:NSIbounds']}). The dashed red curve corresponds to the observational $1\sigma$ bound (Table \ref{['tab:primordial_abundances']}).
• Figure 5: Same as Fig. \ref{['fig:BBN_Yp_2D']}, but for $^2\mathrm{H}/\mathrm{H}$ abundances. The dashed blue curve corresponds to the 1$\sigma$ bound based on the old (2024) best fit for deuterium.