How secret interactions can reconcile sterile neutrinos with cosmology

TL;DR

It is shown that new interactions in the sterile neutrino sector can prevent their production in the early Universe and reconcile short baseline oscillation experiments with cosmology.

Abstract

Short baseline neutrino oscillation experiments have shown hints of the existence of additional sterile neutrinos in the eV mass range. However, such neutrinos seem incompatible with cosmology because they have too large an impact on cosmic structure formation. Here we show that new interactions in the sterile neutrino sector can prevent their production in the early Universe and reconcile short baseline oscillation experiments with cosmology.

Figures (5)

• Figure 1: The evolution of $\Delta N_{\textrm{eff}}$ as the temperature drops for $g_X = 0.1$ and different values of the coupling constant $G_X$.
• Figure 2: Contours of equal thermalization. $\Delta N_{\textrm{eff}}$ is given by the colors. The solid, dashed, and dot-dashed lines correspond to hidden bosons with masses $M_X = 300\:\mega\electronvolt$, $200\:\mega\electronvolt$, and $100\:\mega\electronvolt$ respectively.
• Figure 3: Dependence of $\Delta N_{\textrm{eff}}$ on the mixing parameters. $g_X = 0.01$ has been used for all the models while $G_X$ has been changed to give the variation in mass.
• Figure 4: The sterile energy distribution relative to $f_0$ at $T=4.3\:\mega\electronvolt$, where $\Delta N_{\textrm{eff}}$ crosses 1 for $\delta m^2 = 1\:\electronvolt^2$, $\sin^2(2\theta) = 0.05$, $G_X = G_F$, and $g_X = 0.01$ which corresponds to $M_X = 2.9\:\giga\electronvolt$. Note that the peak at $p/T < 1$ is unimportant due to the limited phase space for so low $p$.
• Figure 5: The active neutrino distribution for different temperatures. The parameters used are $G_X = 3\cdot10^2G_F$ and $g_X=0.025$. This corresponds to a hidden boson with the mass $M_X = 424\:\mega\electronvolt$.