Resolution of puzzles from the LSND, KARMEN, and MiniBooNE experiments

TL;DR

This paper proposes that a heavy sterile neutrino could explain anomalies in neutrino oscillation experiments like LSND, KARMEN, and MiniBooNE, and provides constraints and future search directions for this hypothesis.

Contribution

It introduces a sterile neutrino model that unifies several experimental anomalies and derives parameter ranges consistent with all data, suggesting new experimental searches.

Findings

Heavy neutrino mass range 40-80 MeV

Mixing strength |U_{μh}|^2 ≈ 10^{-3}-10^{-2}

Lifetime τ_{νh} ≲ 10^{-9} s

Abstract

This work has attempted to reconcile puzzling neutrino oscillation results from the LSND, KARMEN and MiniBooNE experiments. We show that the LSND evidence for $\bar{\nu}_\mu \to \bar{\nu}_e$ oscillations, its long-standing disagreement with the results from KARMEN, and the anomalous event excess observed by MiniBooNE in $\nu_\mu$ and $\bar{\nu}_\mu$ data could all be explained by the existence of a heavy sterile neutrino ($\nu_h$). All these results are found to be consistent with each other assuming that the $\nu_h$ is created in $\nu_\mu$ neutral-current interactions and decays radiatively into a photon and a light neutrino. Assuming the $\nu_h$ is produced through mixing with $\nu_\mu$, the combined analysis of the LSND and MiniBooNe excess events suggests that the $\nu_h$ mass is in the range from 40 to 80 MeV, the mixing strength is $|U_{\mu h}|^2 \simeq 10^{-3}-10^{-2}$, and the lifetime is $\tau_{\nu_h} \lesssim 10^{-9}$ s. Surprisingly, this LSND-MiniBooNE parameters window is found to be unconstrained by the results from the most sensitive experiments searching for heavy neutrino. We set new limits on $|U_{\mu h}|^2$ for the LSND-MiniBooNE favorable mass region from the precision measurements of the Michel spectrum by the TWIST experiment. The results obtained provide a strong motivation for a sensitive search for the $\nu_h$ in a near future $ K$ decay or neutrino experiments, which fit well in the existing/planned experimental programs at CERN or FNAL. The question of whether the heavy neutrino is Dirac or Majorana particle is briefly discussed.