Status of 3+1 Neutrino Mixing

TL;DR

The paper addresses short-baseline neutrino oscillations in a 3+1 framework with one sterile neutrino, updating analyses to include the MiniBooNE antineutrino data and MINOS constraints. It finds that a 3+1 description is viable but exhibits tension between appearance and disappearance data, which is alleviated when the MiniBooNE low-energy anomaly is excluded; the global fit yields a best-fit $\\Delta m^2_{41}$ around 5.6 eV$^2$, with additional 1σ regions near 1.6, 1.2, and 0.91 eV$^2$ and small mixing angles. The data suggest that the MiniBooNE low-energy excess may not be due to $\\nu_\mu \\rightarrow \\nu_e$ oscillations, and that a simpler 3+1 interpretation remains preferred over 3+2 in light of cosmological bounds; nevertheless, cosmological bounds challenge large mass-squared values, leaving a narrow viable parameter space. Overall the work clarifies the status of 3+1 mixing, weighing oscillation evidence against cosmology and highlighting targeted directions for future short-baseline tests.

Abstract

We present an update of our analysis of short-baseline neutrino oscillation data in the framework of 3+1 neutrino mixing taking into account the recent update of MiniBooNE antineutrino data and the recent results of the MINOS search for nu_mu disappearance into sterile neutrinos (the more complicated 3+2 neutrino mixing is not needed since the CP-violating difference between MiniBooNE neutrino and antineutrino data has diminished). The results of our fits of short-baseline neutrino oscillation data including the MiniBooNE low-energy anomaly (now present both in the neutrino and antineutrino data) leads to a strong tension between appearance and disappearance data. Hence, it seems likely that the low-energy anomaly is not due to nu_mu -> nu_e transitions. Excluding the MiniBooNE low-energy anomaly, appearance and disappearance data are marginally compatible. The global analysis has the best-fit point at Delta m^2_{41} about 5.6 eV^2, which is rather large in comparison with cosmological bounds, but there are three regions within 1 sigma at Delta m^2_{41} about 1.6, 1.2, 0.91 eV^2. We also show that the data on the Gallium neutrino anomaly favor values of Delta m^2_{41} larger than about 1 eV^2.

Figures (7)

• Figure 1: Allowed regions in the $\sin^{2}2\vartheta_{e\mu}$--$\Delta{m}^2_{41}$ plane obtained from the fit of MiniBooNE antineutrino data 1111.1375Djurcic-NUFACT2011, including the low-energy bins from $200 \, \text{MeV}$ to $475 \, \text{MeV}$. The best-fit point at $\sin^{2}2\vartheta_{e\mu} = 0.005$ and $\Delta{m}^2_{41} = 4.68 \, \text{eV}^2$ is indicated by a cross.
• Figure 2: Allowed regions in the $\sin^{2}2\vartheta_{e\mu}$--$\Delta{m}^2_{41}$ plane obtained from the fit of MiniBooNE antineutrino data with energy $E>475 \, \text{MeV}$1111.1375Djurcic-NUFACT2011. The best-fit point at $\sin^{2}2\vartheta_{e\mu} = 0.0045$ and $\Delta{m}^2_{41} = 4.79 \, \text{eV}^2$ is indicated by a cross.
• Figure 3: Fit of MiniBooNE antineutrino data 1111.1375Djurcic-NUFACT2011 (points with error bars). The red solid line corresponds to the best fit ($\sin^{2}2\vartheta_{e\mu} = 0.005$ and $\Delta{m}^2_{41} = 4.68 \, \text{eV}^2$). The blue dashed and green dotted lines correspond, respectively, to: A: $\sin^{2}2\vartheta_{e\mu} = 0.005$ and $\Delta{m}^2_{41} = 0.8 \, \text{eV}^2$; B: $\sin^{2}2\vartheta_{e\mu} = 0.01$ and $\Delta{m}^2_{41} = 0.5 \, \text{eV}^2$.
• Figure 4: Fit of MINOS data extracted from Ref. 1104.3922. The red solid line corresponds to the best fit ($\sin^{2}2\vartheta_{e\mu} = 0.005$ and $\Delta{m}^2_{41} = 4.68 \, \text{eV}^2$).
• Figure 5: Raster-scan upper bound on $\sin^{2}2\vartheta_{\mu\mu}$ as a function of $\Delta{m}^2_{41}$ plane obtained from the fit of MINOS neutral current data 1104.3922.