How Self-Interactions can Reconcile Sterile Neutrinos with Cosmology

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 of 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.

Figure 1

The evolution of $\mathrm{\Delta }{N}_{\text{eff}}$ as the temperature drops for $g_X=0.1$ and different values of the coupling constant $G_X$.

Figure 2

Contours of equal thermalization. $\mathrm{\Delta }{N}_{\text{eff}}$ is given by the colors. The solid, dashed, and dot-dashed lines correspond to hidden bosons with masses $M_X=300$, 200, and 100 MeV, respectively.

Figure 3

Dependence of $\mathrm{\Delta }{N}_{\text{eff}}$ 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. The standard parameters are ${\sin }^2(2\theta )=0.05$ and $\delta m^2=1{\mathrm{eV}}^2$.

Figure 4

The sterile energy distribution relative to $f_0$ at $T=4.3\mathrm{MeV}$, where $\mathrm{\Delta }{N}_{\text{eff}}$ crosses 1 for $\delta m^2=1{\mathrm{eV}}^2$, ${\sin }^2(2\theta )=0.05$, $G_X=G_F$, and $g_X=0.01$, which corresponds to $M_X=2.9\mathrm{GeV}$.

Figure 5

The active neutrino distribution for different temperatures. The parameters used are $G_X=3\times 10^2{G}_F$ and $g_X=0.025$. This corresponds to a hidden boson with the mass $M_X=424\mathrm{MeV}$.