Effective Matter Flavor Conversion Mediated by Pseudo-Sterile States as the Possible Origin of Neutrino Oscillation Anomalies

Abstract

Neutrino oscillation experiments present anomalous results across a vast range of baselines and energies. Here we show that a 3+1 scenario in which sterile neutrinos feel a novel matter potential $V_s$ proportional to background density of ordinary or (asymmetric) dark matter is able to explain several anomalies. At low-energies ($E\lesssim$ 1 TeV) the model behaves as an effective 3-flavor NSI-like scheme among active flavors and eliminates the tension between the two LBL experiments NOvA and T2K provided that the potential is negative and the two sterile mixing angles ${\theta }_{14}$ and ${\theta }_{24}$ are non-zero. A further indication in favor of a negative non-zero potential comes from the anomalous excess of ${\nu }_e$-like events observed in Super-Kamiokande atmospheric neutrinos, which, in the new scenario is explained by a modification of the 3-flavor resonance at few GeV. A high energies ($E\gtrsim$ 1 TeV) the new framework reveals its 4-flavor nature and produces a resonant behavior at $E\simeq$ 10 TeV as hinted at by IceCube. We identify an irreducible 3-level dynamics generating a new resonance in the $({\nu }_e,{\nu }_{\mu })$ sector intertwined with two conventional resonances in the $({\nu }_e,{\nu }_s$) and $({\nu }_{\mu },{\nu }_s)$ systems. The novel amplification mechanism manifests with the emergence of effective mixing angles in matter (${\theta }_{12}^m$ or ${\theta }_{13}^m$) involving active neutrinos. The scenario requires values of $f=V_s/|V_{NC}|\sim -20$, $\Delta m_{41}^2\sim 60$ eV${}^2$, $|U_{e4}{|}^2\simeq {\sin }^2{\theta }_{14}\simeq 0.01-0.03$ and $|U_{\mu 4}{|}^2\simeq {\sin }^2{\theta }_{24}\simeq 10^{-4}-10^{-3}$. Such a very small size of $|U_{\mu 4}{|}^2$ eliminates the tension between IceCube and the other ${\nu }_{\mu }$ disappearance searches. The model can be directly probed by KATRIN, which is very sensitive to the electron-sterile neutrino admixture in the region of high $\Delta m_{41}^2$.

Comments: 44 pages, 15 Figures, 2 Tables