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^2_{41} \sim 60 $ eV$^2$, $|U_{e4}|^2\simeq \sin^2\theta_{14} \simeq 0.01-0.03$ and $|U_{\mu4}|^2 \simeq \sin^2\theta_{24}\simeq 10^{-4}-10^{-3}$. Such a very small size of $|U_{\mu4}|^2$ 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 $\Delta m^2_{41}$.