Abstract
Searches for light sterile neutrinos are motivated by the unexpected observation of an electron neutrino appearance in short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and the Mini Booster Neutrino Experiment (MiniBooNE). In light of these unexpected results, a campaign using natural and anthropogenic sources to find the light (mass-squared-difference around 1 eV2) sterile neutrinos is underway. Among the natural sources, atmospheric neutrinos provide a unique gateway to search for sterile neutrinos due to the broad range of baseline-to-energy ratios, L/E, and the presence of significant matter effects. Since the atmospheric neutrino flux rapidly falls with energy, studying its highest energy component requires gigaton-scale neutrino detectors. These detectors—often known as neutrino telescopes since they are designed to observe tiny astrophysical neutrino fluxes—have been used to perform searches for light sterile neutrinos, and researchers have found no significant signal to date. This brief review summarizes the current status of searches for light sterile neutrinos with neutrino telescopes deployed in solid and liquid water.
Highlights
Searches for light sterile neutrinos are motivated by the unexpected observation of an electron neutrino appearance in short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and the Mini Booster Neutrino Experiment (MiniBooNE)
A new calculation of the reactor neutrino fluxes put an overall tension of the total normalization for the reactor neutrino experiments [4]—the result was consistent with the measurement from the GALLEX Cr-51 source experiment [5]
Analyses that aim to measure the standard atmospheric neutrino oscillation parameters are sensitive to distortions induced by a light sterile neutrino
Summary
The presence of matter alters neutrino oscillations; for example, differences between the charged- and neutral-current matter potentials play an important role in solar neutrinos [36,37]. In the standard three-neutrino scenario, the effect of the matter potential is small for Earth-traversing neutrinos at the energies typical of atmospheric and longbaseline neutrino experiments. The Earth’s matter effects may significantly enhance the oscillation amplitude between an Earth-traversing standard neutrino and a light, sterile neutrino for neutrinos with energies between 1 and 10 TeV [38,39,40,41,42,43]. Most of the neutrinos that IceCube sees at these energies are produced in cosmic-ray interactions with the atmosphere As a result, these neutrinos are dominantly produced as muon neutrinos. In the 103 GeV–104 GeV range, the substantial disappearance happens due to the enhancement of the probability amplitude arising from the neutral-current matter potential. As will be shown this can be used to place bounds on heavy sterile using the whole energy spectrum [54,55,56]
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